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/generate.py

@@ -28,11 +28,11 @@ nodes_file = (
     .read_text()
 )
 node_lines = (
-    nodes_file.split("pub enum AnyNode {")[1].split("}")[0].strip().splitlines()
+    nodes_file.split("pub enum AnyNodeRef<'a> {")[1].split("}")[0].strip().splitlines()
 )
 nodes = []
 for node_line in node_lines:
-    node = node_line.split("(")[1].split(")")[0].split("::")[-1].split("<")[0]
+    node = node_line.split("(")[1].split(")")[0].split("::")[-1].removeprefix("&'a ")
     # `FString` has a custom implementation while the formatting for
     # `FStringLiteralElement`, `FStringFormatSpec` and `FStringExpressionElement` are handled by the `FString`
     # implementation.