Use dedicated structs in comparable.rs (#5042)

## Summary

Updating to match the updated AST structure, for consistency.

crates/ruff_python_formatter/src/pattern/pattern_match_value.rs

@@ -1,7 +1,9 @@
-use crate::{not_yet_implemented, FormatNodeRule, PyFormatter};
-use ruff_formatter::{write, Buffer, FormatResult};
 use rustpython_parser::ast::PatternMatchValue;
 
+use ruff_formatter::{write, Buffer, FormatResult};
+
+use crate::{not_yet_implemented, FormatNodeRule, PyFormatter};
+
 #[derive(Default)]
 pub struct FormatPatternMatchValue;