Remove lexer-based comment range detection (#5785)

## Summary

I'm doing some unrelated profiling, and I noticed that this method is
actually measurable on the CPython benchmark -- it's > 1% of execution
time. We don't need to lex here, we already know the ranges of all
comments, so we can just do a simple binary search for overlap, which
brings the method down to 0%.

## Test Plan

`cargo test`

crates/ruff_python_ast/src/source_code/indexer.rs

@@ -93,7 +93,7 @@ impl Indexer {
     }
 
     /// Returns the byte offset ranges of comments
-    pub fn comment_ranges(&self) -> &CommentRanges {
+    pub const fn comment_ranges(&self) -> &CommentRanges {
         &self.comment_ranges
     }