fix: skip non-tensor optimizer state entries in distrib_optimizer sav…

[ahmadki]

What does this PR do ?

This is a fix for the TE compatibility issue with the precision-aware optimizer.

_get_main_param_and_optimizer_states (save path) iterates all keys in the optimizer state including non-tensor entries (like found_inf: bool). The save succeeds because get_unscaled_state returns the bool as-is. But on load, _set_main_param_and_optimizer_states passes that same bool to set_scaled_state, which assumes it's a tensor.

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[janEbert]

This semantically includes some of the changes in #3521, but handles more error cases and adds test. I'd thus add this instead of #3521 for the distrib_optimizer stuff, but keep the backward-compatibility tokenizer addition from #3521.

[ahmadki]

/ok to test 6e1d6fa

[ahmadki]

/ok to test 9a0a354

[ahmadki]

/ok to test f2d903f

[svcnvidia-nemo-ci]

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