Reduce size of Expr from 80 to 64 bytes (#9900)

## Summary

This PR reduces the size of `Expr` from 80 to 64 bytes, by reducing the
sizes of...

- `ExprCall` from 72 to 56 bytes, by using boxed slices for `Arguments`.
- `ExprCompare` from 64 to 48 bytes, by using boxed slices for its
various vectors.

In testing, the parser gets a bit faster, and the linter benchmarks
improve quite a bit.

crates/ruff_python_parser/src/parser.rs

@@ -569,8 +569,7 @@ mod tests {
     #[cfg(target_pointer_width = "64")]
     #[test]
     fn size_assertions() {
-        // 80 with Rustc >= 1.76, 88 with Rustc < 1.76
-        assert!(matches!(std::mem::size_of::<ParenthesizedExpr>(), 80 | 88));
+        assert_eq!(std::mem::size_of::<ParenthesizedExpr>(), 72);
     }
 
     #[test]