REFACTOR: move the banner from the rust source to the standard library (#8406)

Related to:
- #8311 
- #8353

# Description
with the new `$nu.startup-time` from #8353 and as mentionned in #8311,
we are now able to fully move the `nushell` banner from the `rust`
source base to the standard library.

this PR
- removes all the `rust` source code for the banner
- rewrites a perfect clone of the banner to `std.nu`, called `std
banner`
- call `std banner` from `default_config.nu`

# User-Facing Changes
see the demo: https://asciinema.org/a/566521

- no config will show the banner (e.g. `cargo run --release --
--no-config-file`)
- a custom config without the `if $env.config.show_banner` block and no
call to `std banner` would never show the banner
- a custom config with the block and `config.show_banner = true` will
show the banner
- a custom config with the block and `config.show_banner = false` will
NOT show the banner

# Tests + Formatting
a new test line has been added to `tests.nu` to check the length of the
`std banner` output.
- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting
```
$nothing
```

---------

Co-authored-by: Darren Schroeder <343840+fdncred@users.noreply.github.com>

src/run.rs

@@ -234,6 +234,7 @@ pub(crate) fn run_repl(
         &mut stack,
         config_files::NUSHELL_FOLDER,
         parsed_nu_cli_args.execute,
+        parsed_nu_cli_args.no_std_lib,
         entire_start_time,
     );
     perf(

src/test_bins.rs

@@ -6,6 +6,7 @@ use nu_engine::eval_block;
 use nu_parser::parse;
 use nu_protocol::engine::{EngineState, Stack, StateWorkingSet};
 use nu_protocol::{CliError, PipelineData, Value};
+use nu_std::load_standard_library;
 // use nu_test_support::fs::in_directory;
 
 /// Echo's value of env keys from args
@@ -175,10 +176,12 @@ pub fn nu_repl() {
     let mut engine_state = nu_cli::add_cli_context(create_default_context());
     let mut stack = Stack::new();
 
-    stack.add_env_var("PWD".to_string(), Value::test_string(cwd.to_string_lossy()));
+    engine_state.add_env_var("PWD".into(), Value::test_string(cwd.to_string_lossy()));
 
     let mut last_output = String::new();
 
+    load_standard_library(&mut engine_state).expect("Could not load the standard library.");
+
     for (i, line) in source_lines.iter().enumerate() {
         let cwd = nu_engine::env::current_dir(&engine_state, &stack)
             .unwrap_or_else(|err| outcome_err(&engine_state, &err));