Remove Int wrapper type from parser (#7577)

## Summary

This is only used for the `level` field in relative imports (e.g., `from
..foo import bar`). It seems unnecessary to use a wrapper here, so this
PR changes to a `u32` directly.

crates/ruff_python_ast/src/comparable.rs

@@ -1161,7 +1161,7 @@ pub struct StmtImport<'a> {
 pub struct StmtImportFrom<'a> {
     module: Option<&'a str>,
     names: Vec<ComparableAlias<'a>>,
-    level: Option<ast::Int>,
+    level: Option<u32>,
 }
 
 #[derive(Debug, PartialEq, Eq, Hash)]