Remove AstNode and AnyNode (#15479)

While looking into potential AST optimizations, I noticed the `AstNode`
trait and `AnyNode` type aren't used anywhere in Ruff or Red Knot. It
looks like they might be historical artifacts of previous ways of
consuming AST nodes?

- `AstNode::cast`, `AstNode::cast_ref`, and `AstNode::can_cast` are not
used anywhere.
- Since `cast_ref` isn't needed anymore, the `Ref` associated type isn't
either.

This is a pure refactoring, with no intended behavior changes.

crates/ruff_python_formatter/src/statement/stmt_while.rs

@@ -1,5 +1,4 @@
 use ruff_formatter::{format_args, write};
-use ruff_python_ast::AstNode;
 use ruff_python_ast::{Stmt, StmtWhile};
 use ruff_text_size::Ranged;
 
@@ -22,7 +21,7 @@ impl FormatNodeRule<StmtWhile> for FormatStmtWhile {
         } = item;
 
         let comments = f.context().comments().clone();
-        let dangling_comments = comments.dangling(item.as_any_node_ref());
+        let dangling_comments = comments.dangling(item);
 
         let body_start = body.first().map_or(test.end(), Stmt::start);
         let or_else_comments_start =