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/pattern/pattern_arguments.rs

@@ -1,5 +1,4 @@
 use ruff_formatter::write;
-use ruff_python_ast::AstNode;
 use ruff_python_ast::{Pattern, PatternArguments};
 use ruff_python_trivia::{SimpleTokenKind, SimpleTokenizer};
 use ruff_text_size::{Ranged, TextRange, TextSize};
@@ -63,7 +62,7 @@ impl FormatNodeRule<PatternArguments> for FormatPatternArguments {
         // )
         // ```
         let comments = f.context().comments().clone();
-        let dangling_comments = comments.dangling(item.as_any_node_ref());
+        let dangling_comments = comments.dangling(item);
 
         write!(
             f,