Update SpeechLM2 for Automodel main

[pzelasko]

Summary

• Update SpeechLM2 to Automodel main at ee0b2261d80d395df7f2dc4767f529cc6b757254 and Megatron-FSDP 0.5.0.
• Migrate distributed loading and model setup to Automodel's public DistributedSetup API.
• Remove obsolete Nemotron-V3 compatibility code and the inline shared-experts patch.
• Raise compatible dependency floors and refresh Docker, configs, docs, tests, and uv.lock.

Validation

• Focused migration tests: 59 passed, 2 skipped.
• isort and Black 24.10.0 checks pass.
• Python syntax compilation and git diff checks pass.
• uv lock --check passes.

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[pzelasko]

/ok to test 3e29e99