Transition to salsa coarse-grained tracked structs (#15763)

## Summary

Transition to using coarse-grained tracked structs (depends on
https://github.com/salsa-rs/salsa/pull/657). For now, this PR doesn't
add any `#[tracked]` fields, meaning that any changes cause the entire
struct to be invalidated. It also changes `AstNodeRef` to be
compared/hashed by pointer address, instead of performing a deep AST
comparison.

## Test Plan

This yields a 10-15% improvement on my machine (though weirdly some runs
were 5-10% without being flagged as inconsistent by criterion, is there
some non-determinism involved?). It's possible that some of this is
unrelated, I'll try applying the patch to the current salsa version to
make sure.

---------

Co-authored-by: Micha Reiser <micha@reiser.io>

crates/ruff_python_ast/src/name.rs

@@ -8,6 +8,7 @@ use crate::{nodes, Expr};
 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Default)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 #[cfg_attr(feature = "cache", derive(ruff_macros::CacheKey))]
+#[cfg_attr(feature = "salsa", derive(salsa::Update))]
 pub struct Name(compact_str::CompactString);
 
 impl Name {