Add the ReservedHashForms2024 rule

This implements the edition 2024 reservations:
  #"
  ##

See rust-lang/rust#123951 (comment)

Author: mattheww

src/lexlucid/pretokenisation/pretokenisation_rules.rs

@@ -29,6 +29,7 @@ enum RuleName {
     LineComment,
     BlockComment,
     UnterminatedBlockComment,
+    ReservedHashForms2024,
     Punctuation,
     SingleQuotedLiteral,
     RawLifetimeOrLabel2021,
@@ -108,6 +109,7 @@ const RULES_FOR_EDITION_2024: &[RuleName] = [
     RuleName::LineComment,
     RuleName::BlockComment,
     RuleName::UnterminatedBlockComment,
+    RuleName::ReservedHashForms2024,
     RuleName::Punctuation,
     RuleName::SingleQuotedLiteral,
     RuleName::RawLifetimeOrLabel2021,
@@ -177,6 +179,14 @@ fn make_named_rules() -> BTreeMap<RuleName, Rule> {
                 / \*
             "##)),
 
+       // Reserved hashes (Rust 2024)
+       (RuleName::ReservedHashForms2024,
+        Rule::new_regex(
+            |_| PretokenData::Reserved, r##"\A
+                \#
+                ( \# | " )
+            "##)),
+
        // Punctuation
        (RuleName::Punctuation,
         Rule::new_regex(

writeup/rules.md

@@ -4,6 +4,7 @@
 [Line comment](#line-comment)\
 [Block comment](#block-comment)\
 [Unterminated block comment](#unterminated-block-comment)\
+[Reserved hash forms (Rust 2024)](#reserved-hash-forms-rust-2024)\
 [Punctuation](#punctuation)\
 [Single-quoted literal](#single-quoted-literal)\
 [Raw lifetime or label (Rust 2021)](#raw-lifetime-or-label-rust-2021)\
@@ -139,6 +140,21 @@ when `character_sequence` represents an iterator over the sequence of characters
 (none)
 
 
+#### Reserved hash forms (Rust 2024) { .rule }
+
+##### Pattern
+```
+\#
+( \# | " )
+```
+
+##### Pretoken kind
+`Reserved`
+
+##### Attributes
+(none)
+
+
 #### Punctuation { .rule }
 
 ##### Pattern