Plan TP=1 with EP>1 simulation fix

[Copilot]

Simulations with TP=1 and EP>1 lose EP/DP_EP group membership and suppress forward/input-gradient EP collectives.

• Root cause
  • SimCCL derives EP/DP_EP groups from TP groups, but omits singleton TP groups.
  • SimAI applies the empty TP dimension mask to EP collectives.
• Proposed changes
  • Represent TP=1 ranks as singleton TP groups in SimCCL.
  • Use data-parallel dimensions for EP forward/input-gradient collectives.
  • Preserve existing TP=1 communicator suppression and TP>1 behavior.
• Scope
  • Analysis and implementation plan only; this PR currently contains no code changes.

• Fixes TP=1,EP>1时仿真失败 #298

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[gabrielecastellano]

The required fix is in the submodule, not in this repository. I have opened PR aliyun/SimCCL#5 with the fix, and it is currently awaiting merge.

Please do not implement an alternative fix in the main repository. Once that PR is merged, update the submodule pointer in this PR to the merged commit containing the fix.