[JAX] Test_multiprocessing_encoder with process spawn in bash

[phu0ngng]

Description

Using the multithreading module which uses os.fork() with JAX which is already multithreading can lead to deadlocks and is not recommended.
This PR removed the usage of multithreading, but spawning processes in a bash script helper.

Type of change

• Documentation change (change only to the documentation, either a fix or a new content)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality not to work as expected)
• Infra/Build change
• Code refactor

Checklist:

• I have read and followed the contributing guidelines
• The functionality is complete
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[phu0ngng]

/te-ci jax