[pmap] Inline `multihost_utils` `impl` functions for host_local <> global conversions, `_shared_code_pmap`, and `_prepare_pmap`.
When `core.trace_state_clean()`, call the `mhu` implementations directly to avoid binding overheads.
Improving the `jax.jit(jax.shard_map)` implementation of `jax.pmap`.
PiperOrigin-RevId: 859185228