[JAX] Bug Fix: WeightInit with field

[phu0ngng]

Description

Nightly CI failed last night with the error:

ValueError: mutable default <class 'praxis.base_layer.WeightInit'> for field bias_init is not allowed: use default_factory

We should not use mutable default value (praxis.base_layer.WeightInit) for bias_init in a dataclass as Python dataclasses don't allow mutable default values to prevent unexpected behavior due to shared state across instances.

This PR fixes the issue by using the default_factory parameter of the field() function from the dataclasses module to create a new object for each instance, avoiding the shared mutable state problem.

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 to not work as expected)
• Infra/Build change
• Code refractor

Changes

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