[Dev] Fix EP Overlap Bugs for Full-Iter CG

[Wohox]

What does this PR do ?

Fix following bugs for full-iter cg:

• Missing stream context for backward dw.
• Memory leak when using HybridEP+FP8.
• Missing record stream for HybridEP's tokens_per_expert.
• Accidentally release the input memory of grouped gemm.

PR for main: #3164

Contribution process

flowchart LR
    A[Pre-checks] --> B[PR Tests]
    subgraph Code Review/Approval
        C1[Expert Review] --> C2[Final Review]
    end
    B --> C1
    C2 --> D[Merge]

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[Wohox]

/ok to test e04d2ce

[Wohox]

/ok to test 8b6ada8

[Wohox]

/ok to test f862dee