Restrict closure expression to be something like {|| ...} (#8290)

# Description

As title, closes: #7921 closes: #8273

# User-Facing Changes

when define a closure without pipe, nushell will raise error for now:
```
❯ let x = {ss ss}
Error: nu::parser::closure_missing_pipe

  × Missing || inside closure
   ╭─[entry #2:1:1]
 1 │ let x = {ss ss}
   ·         ───┬───
   ·            ╰── Parsing as a closure, but || is missing
   ╰────
  help: Try add || to the beginning of closure
```

`any`, `each`, `all`, `where` command accepts closure, it forces user
input closure like `{||`, or parse error will returned.
```
❯ {major:2, minor:1, patch:4} | values | each { into string }
Error: nu::parser::closure_missing_pipe

  × Missing || inside closure
   ╭─[entry #4:1:1]
 1 │ {major:2, minor:1, patch:4} | values | each { into string }
   ·                                             ───────┬───────
   ·                                                    ╰── Parsing as a closure, but || is missing
   ╰────
  help: Try add || to the beginning of closure
```

`with-env`, `do`, `def`, `try` are special, they still remain the same,
although it says that it accepts a closure, but they don't need to be
written like `{||`, it's more likely a block but can capture variable
outside of scope:
```
❯ def test [input] { echo [0 1 2] | do { do { echo $input } } }; test aaa
aaa
```

Just realize that It's a big breaking change, we need to update config
and scripts...

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `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

# 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.

crates/nu-utils/src/sample_config/default_config.nu

@@ -12,7 +12,7 @@ let dark_theme = {
     empty: blue
     # Closures can be used to choose colors for specific values.
     # The value (in this case, a bool) is piped into the closure.
-    bool: { if $in { 'light_cyan' } else { 'light_gray' } }
+    bool: {|| if $in { 'light_cyan' } else { 'light_gray' } }
     int: white
     filesize: {|e|
       if $e == 0b {
@@ -22,7 +22,7 @@ let dark_theme = {
       } else { 'blue' }
     }
     duration: white
-    date: { (date now) - $in |
+    date: {|| (date now) - $in |
       if $in < 1hr {
         'red3b'
       } else if $in < 6hr {
@@ -93,7 +93,7 @@ let light_theme = {
     empty: blue
     # Closures can be used to choose colors for specific values.
     # The value (in this case, a bool) is piped into the closure.
-    bool: { if $in { 'dark_cyan' } else { 'dark_gray' } }
+    bool: {|| if $in { 'dark_cyan' } else { 'dark_gray' } }
     int: dark_gray
     filesize: {|e|
       if $e == 0b {
@@ -103,7 +103,7 @@ let light_theme = {
       } else { 'blue_bold' }
     }
     duration: dark_gray
-  date: { (date now) - $in |
+  date: {|| (date now) - $in |
     if $in < 1hr {
       'red3b'
     } else if $in < 6hr {
@@ -289,10 +289,10 @@ let-env config = {
   render_right_prompt_on_last_line: false # true or false to enable or disable right prompt to be rendered on last line of the prompt.
 
   hooks: {
-    pre_prompt: [{
+    pre_prompt: [{||
       null  # replace with source code to run before the prompt is shown
     }]
-    pre_execution: [{
+    pre_execution: [{||
       null  # replace with source code to run before the repl input is run
     }]
     env_change: {
@@ -300,7 +300,7 @@ let-env config = {
         null  # replace with source code to run if the PWD environment is different since the last repl input
       }]
     }
-    display_output: {
+    display_output: {||
       if (term size).columns >= 100 { table -e } else { table }
     }
   }

crates/nu-utils/src/sample_config/default_env.nu

@@ -33,15 +33,15 @@ def create_right_prompt [] {
 }
 
 # Use nushell functions to define your right and left prompt
-let-env PROMPT_COMMAND = { create_left_prompt }
-let-env PROMPT_COMMAND_RIGHT = { create_right_prompt }
+let-env PROMPT_COMMAND = {|| create_left_prompt }
+let-env PROMPT_COMMAND_RIGHT = {|| create_right_prompt }
 
 # The prompt indicators are environmental variables that represent
 # the state of the prompt
-let-env PROMPT_INDICATOR = { "> " }
-let-env PROMPT_INDICATOR_VI_INSERT = { ": " }
-let-env PROMPT_INDICATOR_VI_NORMAL = { "> " }
-let-env PROMPT_MULTILINE_INDICATOR = { "::: " }
+let-env PROMPT_INDICATOR = {|| "> " }
+let-env PROMPT_INDICATOR_VI_INSERT = {|| ": " }
+let-env PROMPT_INDICATOR_VI_NORMAL = {|| "> " }
+let-env PROMPT_MULTILINE_INDICATOR = {|| "::: " }
 
 # Specifies how environment variables are:
 # - converted from a string to a value on Nushell startup (from_string)

crates/nu-utils/src/sample_config/sample_login.nu

@@ -3,7 +3,7 @@
 # - will be sourced after config.nu and env.nu in case of nushell started as login shell
 
 # just as an example for overwriting of an environment variable of env.nu
-let-env PROMPT_INDICATOR = { "(LS)> " }
+let-env PROMPT_INDICATOR = {|| "(LS)> " }
 
 # Similar to env-path and config-path there is a variable containing the path to login.nu
 echo $nu.loginshell-path