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_ast/src/node.rs

@@ -2588,7 +2588,7 @@ impl AstNode for ast::ExprCompare {
 
         visitor.visit_expr(left);
 
-        for (op, comparator) in ops.iter().zip(comparators) {
+        for (op, comparator) in ops.iter().zip(&**comparators) {
             visitor.visit_cmp_op(op);
             visitor.visit_expr(comparator);
         }