Use cursor offset for lexer checkpoint (#11734)

## Summary

This PR updates the lexer checkpoint to store the cursor offset instead
of cloning the cursor itself. This reduces the size of `LexerCheckpoint`
from 136 to 112 bytes and also removes the need for lifetime.

## Test Plan

`cargo insta test`

Author: dhruvmanila

crates/ruff_python_parser/src/lexer.rs

@@ -1338,13 +1338,13 @@ impl<'src> Lexer<'src> {
     }
 
     /// Creates a checkpoint to which the lexer can later return to using [`Self::rewind`].
-    pub(crate) fn checkpoint(&self) -> LexerCheckpoint<'src> {
+    pub(crate) fn checkpoint(&self) -> LexerCheckpoint {
         LexerCheckpoint {
             value: self.current_value.clone(),
             current_kind: self.current_kind,
             current_range: self.current_range,
             current_flags: self.current_flags,
-            cursor: self.cursor.clone(),
+            cursor_offset: self.offset(),
             state: self.state,
             nesting: self.nesting,
             indentations_checkpoint: self.indentations.checkpoint(),
@@ -1355,13 +1355,13 @@ impl<'src> Lexer<'src> {
     }
 
     /// Restore the lexer to the given checkpoint.
-    pub(crate) fn rewind(&mut self, checkpoint: LexerCheckpoint<'src>) {
+    pub(crate) fn rewind(&mut self, checkpoint: LexerCheckpoint) {
         let LexerCheckpoint {
             value,
             current_kind,
             current_range,
             current_flags,
-            cursor,
+            cursor_offset,
             state,
             nesting,
             indentations_checkpoint,
@@ -1370,6 +1370,10 @@ impl<'src> Lexer<'src> {
             errors_position,
         } = checkpoint;
 
+        let mut cursor = Cursor::new(self.source);
+        // We preserve the previous char using this method.
+        cursor.skip_bytes(cursor_offset.to_usize());
+
         self.current_value = value;
         self.current_kind = current_kind;
         self.current_range = current_range;
@@ -1700,12 +1704,12 @@ pub(crate) enum TokenValue {
     },
 }
 
-pub(crate) struct LexerCheckpoint<'src> {
+pub(crate) struct LexerCheckpoint {
     value: TokenValue,
     current_kind: TokenKind,
     current_range: TextRange,
     current_flags: TokenFlags,
-    cursor: Cursor<'src>,
+    cursor_offset: TextSize,
     state: State,
     nesting: u32,
     indentations_checkpoint: IndentationsCheckpoint,

crates/ruff_python_parser/src/parser/mod.rs

@@ -609,7 +609,7 @@ impl<'src> Parser<'src> {
     }
 
     /// Creates a checkpoint to which the parser can later return to using [`Self::rewind`].
-    fn checkpoint(&self) -> ParserCheckpoint<'src> {
+    fn checkpoint(&self) -> ParserCheckpoint {
         ParserCheckpoint {
             tokens: self.tokens.checkpoint(),
             errors_position: self.errors.len(),
@@ -620,7 +620,7 @@ impl<'src> Parser<'src> {
     }
 
     /// Restore the parser to the given checkpoint.
-    fn rewind(&mut self, checkpoint: ParserCheckpoint<'src>) {
+    fn rewind(&mut self, checkpoint: ParserCheckpoint) {
         let ParserCheckpoint {
             tokens,
             errors_position,
@@ -637,8 +637,8 @@ impl<'src> Parser<'src> {
     }
 }
 
-struct ParserCheckpoint<'src> {
-    tokens: TokenSourceCheckpoint<'src>,
+struct ParserCheckpoint {
+    tokens: TokenSourceCheckpoint,
     errors_position: usize,
     current_token_id: TokenId,
     prev_token_end: TextSize,

crates/ruff_python_parser/src/token_source.rs

@@ -126,7 +126,7 @@ impl<'src> TokenSource<'src> {
     }
 
     /// Creates a checkpoint to which the token source can later return to using [`Self::rewind`].
-    pub(crate) fn checkpoint(&self) -> TokenSourceCheckpoint<'src> {
+    pub(crate) fn checkpoint(&self) -> TokenSourceCheckpoint {
         TokenSourceCheckpoint {
             lexer_checkpoint: self.lexer.checkpoint(),
             tokens_position: self.tokens.len(),
@@ -135,7 +135,7 @@ impl<'src> TokenSource<'src> {
     }
 
     /// Restore the token source to the given checkpoint.
-    pub(crate) fn rewind(&mut self, checkpoint: TokenSourceCheckpoint<'src>) {
+    pub(crate) fn rewind(&mut self, checkpoint: TokenSourceCheckpoint) {
         let TokenSourceCheckpoint {
             lexer_checkpoint,
             tokens_position,
@@ -168,8 +168,8 @@ impl<'src> TokenSource<'src> {
     }
 }
 
-pub(crate) struct TokenSourceCheckpoint<'src> {
-    lexer_checkpoint: LexerCheckpoint<'src>,
+pub(crate) struct TokenSourceCheckpoint {
+    lexer_checkpoint: LexerCheckpoint,
     tokens_position: usize,
     comments_position: usize,
 }