Add more elasticity goodput tests

[dipannita08]

Description

This PR adds:

• More elasticity + goodput tests
• Tightens the check for backend pathways and elasticity enabled.
• Adds some useful debugging logs
• Minor cleanups.

Tests

• Run all tests locally.
• E2E MaxText run with pathways elasticity enabled.

Checklist

Before submitting this PR, please make sure (put X in square brackets):

• I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run end-to-end tests tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed, including adding new documentation pages to the relevant Table of Contents (toctree directive) as explained in our documentation.

[gemini-code-assist]

Code Review

This pull request refactors the goodput monitoring and recording logic to safely resolve and fall back to base monitors and recorders when elastic features are disabled or fail to load. It also introduces hasattr checks in elastic_utils.py to prevent errors when interacting with recorders that lack elastic APIs, accompanied by comprehensive unit tests. The reviewer suggested ensuring that both record_elastic_wait_end_time and record_elastic_reinit_start_time are checked before invocation to prevent potential AttributeErrors.

[gemini-code-assist]

To ensure robust defensive programming, we should verify that the recorder implements both record_elastic_wait_end_time and record_elastic_reinit_start_time before calling them. Currently, we only check for the presence of record_elastic_wait_end_time, which could lead to an AttributeError if a custom or mock recorder only implements one of the methods.

Suggested change

	if recorder and hasattr(recorder, "record_elastic_wait_end_time"):
	recorder.record_elastic_wait_end_time(event_type=event_type)
	recorder.record_elastic_reinit_start_time()
	record_slice_state(recorder)
	if (
	recorder
	and hasattr(recorder, "record_elastic_wait_end_time")
	and hasattr(recorder, "record_elastic_reinit_start_time")
	):
	recorder.record_elastic_wait_end_time(event_type=event_type)
	recorder.record_elastic_reinit_start_time()
	record_slice_state(recorder)

[codecov]

Codecov Report

❌ Patch coverage is 7.40741% with 25 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/maxtext/common/goodput.py	4.34%	22 Missing ⚠️
src/maxtext/utils/elastic_utils.py	25.00%	2 Missing and 1 partial ⚠️

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