Add argument for setting inference logits dtype

[santhnm2]

What does this PR do ?

The inference logits dtype previously relied implicitly on Float16Module defaulting fp32_output to True to ensure fp32 logits. Also, the pipeline parallel path converted logits to params_dtype for buffer dtype consistency. Now everything is standardized around --inference-logits-dtype which defaults to fp32 and is used explicitly.

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[santhnm2]

/ok to test b7542b7

[santhnm2]

/ok to test 665ec48