Fix RL sequence packing bin size

[tdene]

What does this PR do ?

The argument --rl-sequence-packing-max-sequences-per-bin was changed from its default of 50 to 32 because empirical testing showed a speed-up in iteration time.

The value of this argument determines how many no-ops the cu_seqlen tensor that gets fed into TE's RoPE kernels may be padded with. Unfortunately, such no-ops still take execution time, slowing down the overall iteration. Reducing the total number of ops from 50 to 32 speeds up iteration.

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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[jalbericiola]

LGTM