jax

2d1bc5c2 - Refactor Jax FFI lowering to prepare for implementing CPU/GPU callbacks using XLA's FFI.

Refactor Jax FFI lowering to prepare for implementing CPU/GPU callbacks using XLA's FFI. - This refactor just moves code around and should have no impact on tests or public-facing APIs. - `mlir.emit_python_callback` would eventually depend on `ffi.ffi_lowering`, which in turn depends on definitions in `mlir.py`. We break this circular dependency. PiperOrigin-RevId: 729561359