[Roll forward -- Take 2] Optimize large JAX Mesh construction #40785

[Roll forward -- Take 2] Optimize large JAX Mesh construction

• Avoid intermediate tuple -> np.ndarray reallocation: Previously Mesh._create took flat_devices_tuple and reallocated an np.ndarray via np.array(flat_devices_tuple).reshape(device_shape). We now introduce _HashableDeviceArray wrapping the original np.ndarray and xc.DeviceList, avoiding the array reallocation.


• Reuse xc.DeviceList: Cache _cached_device_list on the Mesh instance during construction and return it directly from the _internal_device_list property, avoiding redundant DeviceList allocations.

Reverts 008c954b905e7119157f55dc6ea7d16ee15ce05f