[pyupgrade] Do not report when a UTF-8 comment is followed by a non-UTF-8 one (UP009) (#14728)

## Summary

Resolves #14704.

## Test Plan

`cargo nextest run` and `cargo insta test`.

---------

Co-authored-by: Micha Reiser <micha@reiser.io>

crates/ruff_source_file/src/line_ranges.rs

@@ -295,6 +295,44 @@ pub trait LineRanges {
     /// ## Panics
     /// If the start or end of `range` is out of bounds.
     fn full_lines_str(&self, range: TextRange) -> &str;
+
+    /// The number of lines `range` spans.
+    ///
+    /// ## Examples
+    ///
+    /// ```
+    /// # use ruff_text_size::{Ranged, TextRange};
+    /// # use ruff_source_file::LineRanges;
+    ///
+    /// assert_eq!("a\nb".count_lines(TextRange::up_to(1.into())), 0);
+    /// assert_eq!("a\nb\r\nc".count_lines(TextRange::up_to(3.into())), 1, "Up to the end of the second line");
+    /// assert_eq!("a\nb\r\nc".count_lines(TextRange::up_to(4.into())), 2, "In between the line break characters");
+    /// assert_eq!("a\nb\r\nc".count_lines(TextRange::up_to(5.into())), 2);
+    /// assert_eq!("Single line".count_lines(TextRange::up_to(13.into())), 0);
+    /// assert_eq!("out\nof\nbounds end".count_lines(TextRange::up_to(55.into())), 2);
+    /// ```
+    fn count_lines(&self, range: TextRange) -> u32 {
+        let mut count = 0;
+        let mut line_end = self.line_end(range.start());
+
+        loop {
+            let next_line_start = self.full_line_end(line_end);
+
+            // Reached the end of the string
+            if next_line_start == line_end {
+                break count;
+            }
+
+            // Range ends at the line boundary
+            if line_end >= range.end() {
+                break count;
+            }
+
+            count += 1;
+
+            line_end = self.line_end(next_line_start);
+        }
+    }
 }
 
 impl LineRanges for str {