[syntax-errors] nonlocal declaration at module level (#17559)

## Summary

Part of #17412

Add a new compile-time syntax error for detecting `nonlocal`
declarations at a module level.

## Test Plan

- Added new inline tests for the syntax error
- Updated existing tests for `nonlocal` statement parsing to be inside a
function scope

Co-authored-by: Brent Westbrook <36778786+ntBre@users.noreply.github.com>

crates/ruff_python_parser/tests/fixtures.rs

@@ -538,7 +538,7 @@ impl SemanticSyntaxContext for SemanticSyntaxCheckerVisitor<'_> {
     }
 
     fn in_module_scope(&self) -> bool {
-        true
+        self.scopes.len() == 1
     }
 
     fn in_function_scope(&self) -> bool {