feat: Support custom layer for Python binding.

For now, we already have custom layer support in the OpenDAL core to allow people hook the operation process lifecycle.

I think we may support the custom layer in Python to allow people register the Python callback in the custom layer?

Start by reviewing the existing custom layer support in the OpenDAL core and the Python binding implementation. Determine how Python callbacks should be registered and invoked across the operation lifecycle, then define the behavior and tests needed to demonstrate that custom layers work from Python.

Written by the indexing model from the issue text.