[TEST] Jax separate networks update components

[RuanJohn]

What do you want to test?

Unit test for the MAPGEpochUpdateSeparateNetworks and MAPGMinibatchUpdateSeparateNetworks components of the Jax PPO implementation that makes use of separate critic and policy netowrks.

Outline of test structure

• Unit tests
• Test components and hooks

Definition of done

Passing checks, cover all hooks, edge cases considered

Mandatory checklist before making a PR

• [ ] The success criteria laid down in “Definition of done” are met.
• [ ] Test code is documented - docstrings for methods and classes, static types for arguments.
• [ ] Documentation is updated - README, CONTRIBUTING, or other documentation.