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/expression/expr_slice.rs

@@ -1,5 +1,5 @@
 use ruff_formatter::{write, FormatError};
-use ruff_python_ast::{AnyNodeRef, AstNode};
+use ruff_python_ast::AnyNodeRef;
 use ruff_python_ast::{Expr, ExprSlice, ExprUnaryOp, UnaryOp};
 use ruff_python_trivia::{SimpleToken, SimpleTokenKind, SimpleTokenizer};
 use ruff_text_size::{Ranged, TextRange};
@@ -36,7 +36,7 @@ impl FormatNodeRule<ExprSlice> for FormatExprSlice {
         // to handle newlines and spacing, or the node is None and we insert the corresponding
         // slice of dangling comments
         let comments = f.context().comments().clone();
-        let slice_dangling_comments = comments.dangling(item.as_any_node_ref());
+        let slice_dangling_comments = comments.dangling(item);
         // Put the dangling comments (where the nodes are missing) into buckets
         let first_colon_partition_index =
             slice_dangling_comments.partition_point(|x| x.start() < first_colon.start());

crates/ruff_python_formatter/src/expression/expr_subscript.rs

@@ -1,5 +1,5 @@
 use ruff_formatter::{write, FormatRuleWithOptions};
-use ruff_python_ast::{AnyNodeRef, AstNode};
+use ruff_python_ast::AnyNodeRef;
 use ruff_python_ast::{Expr, ExprSubscript};
 
 use crate::expression::expr_tuple::TupleParentheses;
@@ -35,7 +35,7 @@ impl FormatNodeRule<ExprSubscript> for FormatExprSubscript {
         let call_chain_layout = self.call_chain_layout.apply_in_node(item, f);
 
         let comments = f.context().comments().clone();
-        let dangling_comments = comments.dangling(item.as_any_node_ref());
+        let dangling_comments = comments.dangling(item);
         debug_assert!(
             dangling_comments.len() <= 1,
             "A subscript expression can only have a single dangling comment, the one after the bracket"