FEATURE: wrap the dev instructions from the PR template for easier use (#8152)

i was writing #8148 and came to the "_Test + Formatting_" section of the
PR template.
i felt the developer instructions could be wrapped up in a common easy
to use format, e.g. a `Makefile`, to be used with a few-words command
only, e.g. `make fmt` or `make clippy`, instead of the long commands in
the PR template 🤔

> **Note**
> in case you guys do not want to add a `Makefile` to the `nushell`
source, that PR can be discarded 😌

# Description
this PR
- adds the few rules from the PR template to a new `Makefile`
- replaces the instructions in the PR template from the full commands to
the new `make` rules

# User-Facing Changes
- _none for the regular user_
- i believe easier to test PRs for the developer, allowing one not to
realy on knowing the long commands or using the shell history to run
them again 😋

# Tests + Formatting
_nothing to test_

# After Submitting
maybe mention that in `CONTRIBUTING.md`?

.github/pull_request_template.md

@@ -19,6 +19,13 @@ Make sure you've run and fixed any issues with these commands:
 - `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A clippy::needless_collect` to check that you're using the standard code style
 - `cargo test --workspace` to check that all tests pass
 
+> **Note**
+> from `nushell` you can also use the `toolkit` as follows
+> ```bash
+> use toolkit.nu  # or use an `env_change` hook to activate it automatically
+> toolkit check pr
+> ```
+
 # After Submitting
 
 If your PR had any user-facing changes, update [the documentation](https://github.com/nushell/nushell.github.io) after the PR is merged, if necessary. This will help us keep the docs up to date.

toolkit.nu

@@ -0,0 +1,141 @@
+# this module regroups a bunch of development tools to make the development
+# process easier for anyone.
+#
+# the main purpose of `toolkit` is to offer an easy to use interface for the
+# developer during a PR cycle, namely to (**1**) format the source base,
+# (**2**) catch classical flaws in the new changes with *clippy* and (**3**)
+# make sure all the tests pass.
+
+# check standard code formatting and apply the changes
+export def fmt [
+    --check: bool  # do not apply the format changes, only check the syntax
+] {
+    if ($check) {
+        cargo fmt --all -- --check
+    } else {
+        cargo fmt --all
+    }
+}
+
+# check that you're using the standard code style
+#
+# > it is important to make `clippy` happy :relieved:
+export def clippy [] {
+    cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A clippy::needless_collect
+}
+
+# check that all the tests pass
+export def test [
+    --fast: bool  # use the "nextext" `cargo` subcommand to speed up the tests (see [`cargo-nextest`](https://nexte.st/) and [`nextest-rs/nextest`](https://github.com/nextest-rs/nextest))
+] {
+    if ($fast) {
+        cargo nextest --workspace
+    } else {
+        cargo test --workspace
+    }
+}
+
+# run all the necessary checks and tests to submit a perfect PR
+#
+# # Example
+# let us say we apply a change that
+# - breaks the formatting, e.g. with extra newlines everywhere
+# - makes clippy sad, e.g. by adding unnecessary string conversions with `.to_string()`
+# - breaks the tests by output bad string data from a data structure conversion
+#
+# > the following diff breaks all of the three checks!
+# > ```diff
+# > diff --git a/crates/nu-command/src/formats/to/nuon.rs b/crates/nu-command/src/formats/to/nuon.rs
+# > index abe34c054..927d6a3de 100644
+# > --- a/crates/nu-command/src/formats/to/nuon.rs
+# > +++ b/crates/nu-command/src/formats/to/nuon.rs
+# > @@ -131,7 +131,8 @@ pub fn value_to_string(v: &Value, span: Span) -> Result<String, ShellError> {
+# >                          }
+# >                      })
+# >                      .collect();
+# > -                let headers_output = headers.join(", ");
+# > +                let headers_output = headers.join(&format!("x {}", "")
+# > +                    .to_string());
+# >
+# >                  let mut table_output = vec![];
+# >                  for val in vals {
+# > ```
+#
+# - we run the toolkit once and it fails...
+# ```nushell
+# >_ toolkit check pr
+# running `toolkit fmt`
+# Diff in /home/amtoine/.local/share/git/store/github.com/amtoine/nushell/crates/nu-command/src/formats/to/nuon.rs at line 131:
+#                          }
+#                      })
+#                      .collect();
+# -                let headers_output = headers.join(&format!("x {}", "")
+# -                    .to_string());
+# +                let headers_output = headers.join(&format!("x {}", "").to_string());
+#
+#                  let mut table_output = vec![];
+#                  for val in vals {
+#
+# please run toolkit fmt to fix the formatting
+# ```
+# - we run `toolkit fmt` as proposed and rerun the toolkit... to see clippy is sad...
+# ```nushell
+# running `toolkit fmt`
+# running `toolkit clippy`
+# ...
+# error: redundant clone
+#    --> crates/nu-command/src/formats/to/nuon.rs:134:71
+#     |
+# 134 |                 let headers_output = headers.join(&format!("x {}", "").to_string());
+#     |                                                                       ^^^^^^^^^^^^ help: remove this
+#     |
+# note: this value is dropped without further use
+#    --> crates/nu-command/src/formats/to/nuon.rs:134:52
+#     |
+# 134 |                 let headers_output = headers.join(&format!("x {}", "").to_string());
+#     |                                                    ^^^^^^^^^^^^^^^^^^^
+#     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_clone
+#     = note: `-D clippy::redundant-clone` implied by `-D warnings`
+#
+# error: could not compile `nu-command` due to previous error
+# ```
+# - we remove the useless `.to_string()`, and in that cases, the whole format is useless, only `"x "` is usefull!
+# but now the tests do not pass :sob:
+# ```nushell
+# running `toolkit fmt`
+# running `toolkit clippy`
+# ...
+# running `toolkit test`
+# ...
+# failures:
+#     commands::insert::insert_uses_enumerate_index
+#     commands::merge::multi_row_table_overwrite
+#     commands::merge::single_row_table_no_overwrite
+#     commands::merge::single_row_table_overwrite
+#     commands::update::update_uses_enumerate_index
+#     commands::upsert::upsert_uses_enumerate_index_inserting
+#     commands::upsert::upsert_uses_enumerate_index_updating
+#     commands::where_::where_uses_enumerate_index
+#     format_conversions::nuon::does_not_quote_strings_unnecessarily
+#     format_conversions::nuon::to_nuon_table
+# ```
+# - finally let's fix the tests by removing the `x`, essentially removing the whole diff we applied at the top!
+#
+# now the whole `toolkit check pr` passes! :tada:
+export def "check pr" [
+    --fast: bool  # use the "nextext" `cargo` subcommand to speed up the tests (see [`cargo-nextest`](https://nexte.st/) and [`nextest-rs/nextest`](https://github.com/nextest-rs/nextest))
+] {
+    print "running `toolkit fmt`"
+    try {
+        fmt --check
+    } catch {
+        print $"\nplease run (ansi default_dimmed)(ansi default_italic)toolkit fmt(ansi reset) to fix the formatting"
+        return
+    }
+
+    print "running `toolkit clippy`"
+    clippy
+
+    print "running `toolkit test`"
+    if $fast { test --fast } else { test }
+}