test: introduce "run_first" marker to fail on config changes early

[terrykong]

What does this PR do ?

Add a marker called run_first to force some tests that fail often first. This includes config and recipe tests.

Also at the same time fix up #863

Issues

List issues that this PR closes (syntax):

Closes #863

Usage

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[github-actions]

ℹ️ File Consistency Check

Check based on commit: d0576b2 (PR #993 from tk/test-qol)

✅ DTensor Policy Worker Synchronization Check

Both DTensor policy worker files were modified in this PR:

• nemo_rl/models/policy/dtensor_policy_worker.py
• nemo_rl/models/policy/dtensor_policy_worker_v2.py

Please ensure that the changes are consistent between both files where applicable.

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