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_with.rs

@@ -1,6 +1,5 @@
 use ruff_formatter::{format_args, write, FormatContext, FormatError};
-use ruff_python_ast::StmtWith;
-use ruff_python_ast::{AstNode, WithItem};
+use ruff_python_ast::{StmtWith, WithItem};
 use ruff_python_trivia::{SimpleTokenKind, SimpleTokenizer};
 use ruff_text_size::{Ranged, TextRange};
 
@@ -36,7 +35,7 @@ impl FormatNodeRule<StmtWith> for FormatStmtWith {
         //     ...
         // ```
         let comments = f.context().comments().clone();
-        let dangling_comments = comments.dangling(with_stmt.as_any_node_ref());
+        let dangling_comments = comments.dangling(with_stmt);
         let partition_point = dangling_comments.partition_point(|comment| {
             with_stmt
                 .items