Split weakref_lru_cache into its own extension.
Now that https://github.com/jax-ml/jax/commit/db11efab3be59105b2ac2ccce7281fda30438f1d has landed, we're free to split up xla_extension without creating binary size problems or having to be quite so careful about cross-module dependencies. Here weakref_lru_cache has absolutely nothing to do with XLA.
There's no reason weakref_lru_cache is in the same Python extension as everything else.
PiperOrigin-RevId: 745271825