Onboard explicit sharding to deepseek

[NuojCheng]

Description

In this PR we made following changes:

1. Add sharding constraints/reshards for explicit sharding bug-free;
2. Add attention tests on explicit sharding, including expert parallelism, context parallelism, and mixture of two

Tests

Model_name: deepseek3-test
TL;DR:

Full FSDP

• 8d9588a: xprof
• shard_mode=auto: xprof
• shard_mode=explicit: xprof

FSDP + TP

• 8d9588a: xprof
• shard_mode=auto: xprof
• shard_mode=explicit: xprof

FSDP + CP

• 8d9588a: xprof
• shard_mode=auto: xprof
• shard_mode=explicit: xprof

Checklist

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• 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.