For # to start a comment, then it either need to be the first chara… (#14562)

This PR should close
1. #10327 
1. #13667 
1. #13810 
1. #14129 

# Description
For `#` to start a comment, then it either need to be the first
character of the token or prefixed with ` ` (space).

So now you can do this:
``` 
~/Projects/nushell> 1..10 | each {echo test#testing }                                                                                                                     12/05/2024 05:37:19 PM
╭───┬──────────────╮
│ 0 │ test#testing │
│ 1 │ test#testing │
│ 2 │ test#testing │
│ 3 │ test#testing │
│ 4 │ test#testing │
│ 5 │ test#testing │
│ 6 │ test#testing │
│ 7 │ test#testing │
│ 8 │ test#testing │
│ 9 │ test#testing │
╰───┴──────────────╯
```  

# User-Facing Changes
It is a breaking change if anyone expected comments to start in the
middle of a string without any prefixing ` ` (space).

# Tests + Formatting
Did all: 
- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used` to
check that you're using the standard code style
- `cargo test --workspace` to check that all tests pass (on Windows make
sure to [enable developer
mode](https://learn.microsoft.com/en-us/windows/apps/get-started/developer-mode-features-and-debugging))
- `cargo run -- -c "use toolkit.nu; toolkit test stdlib"` to run the
tests for the standard library

# After Submitting
I cant see that I need to update anything in [the
documentation](https://github.com/nushell/nushell.github.io) but please
point me in the direction if there is anything.

crates/nu-parser/tests/test_lex.rs

@@ -159,6 +159,29 @@ fn lex_comment() {
     );
 }
 
+#[test]
+fn lex_not_comment_needs_space_in_front_of_hashtag() {
+    let file = b"1..10 | each {echo test#testing }";
+
+    let output = lex(file, 0, &[], &[], false);
+
+    assert!(output.1.is_none());
+}
+
+#[test]
+fn lex_comment_with_space_in_front_of_hashtag() {
+    let file = b"1..10 | each {echo test #testing }";
+
+    let output = lex(file, 0, &[], &[], false);
+
+    assert!(output.1.is_some());
+    assert!(matches!(
+        output.1.unwrap(),
+        ParseError::UnexpectedEof(missing_token, span) if missing_token == "}"
+            && span == Span::new(33, 34)
+    ));
+}
+
 #[test]
 fn lex_is_incomplete() {
     let file = b"let x = 300 | ;";