Move {AnyNodeRef, AstNode} to ruff_python_ast crate root (#8030)

This is a do-over of https://github.com/astral-sh/ruff/pull/8011, which
I accidentally merged into a non-`main` branch. Sorry!

crates/ruff_python_formatter/src/statement/stmt_nonlocal.rs

@@ -1,5 +1,5 @@
 use ruff_formatter::{format_args, write};
-use ruff_python_ast::node::AstNode;
+use ruff_python_ast::AstNode;
 use ruff_python_ast::StmtNonlocal;
 
 use crate::comments::{SourceComment, SuppressionKind};