modelopt=0.21.0 update
[🤖]: Hi @janekl 👋,

We wanted to let you know that a [CICD pipeline](https://github.com/NVIDIA/NeMo/actions/runs/12262653049) for this PR just finished successfully

So it might be time to merge this PR or get some approvals

I'm just a bot so I'll leave it you what to do next.

//cc @pablo-garay @ko3n1g > Why is modelopt not part of requirements txt?

I think Eric wanted it to be only an optional requirement for NeMo in the initial integration effort (see [here](https://github.com/NVIDIA/NeMo/pull/8444#discussion_r1514770391) and [here](https://github.com/NVIDIA/NeMo/pull/8444/commits/ae88e4744e43f0c7afc7d6bc8739a42a05a18209#r1514771010)). It's also import guarded (see [here](https://github.com/NVIDIA/NeMo/blob/main/nemo/collections/llm/quantization/quantizer.py#L34-L51), for example).

Are you suggesting to revisit this decision? > > Why is modelopt not part of requirements txt?
> 
> I think Eric wanted it to be only an optional requirement for NeMo in the initial integration effort (see [here](https://github.com/NVIDIA/NeMo/pull/8444#discussion_r1514770391) and [here](https://github.com/NVIDIA/NeMo/pull/8444/commits/ae88e4744e43f0c7afc7d6bc8739a42a05a18209#r1514771010)). It's also import guarded (see [here](https://github.com/NVIDIA/NeMo/blob/main/nemo/collections/llm/quantization/quantizer.py#L34-L51), for example).
> 
> Are you suggesting to revisit this decision?

If this was for initial implementation then yes, let’s revisit it. But not necessarily as part of this PR. Thanks for explaining! This needs to be synced with an update on container side, I'll let you know once ready [🤖]: Hi @janekl 👋,

We wanted to let you know that a [CICD pipeline](https://github.com/NVIDIA/NeMo/actions/runs/12549035693) for this PR just finished successfully

So it might be time to merge this PR or get some approvals

I'm just a bot so I'll leave it you what to do next.

//cc @pablo-garay @ko3n1g
# What does this PR do ?

* ~~Bugfix to correctly support Mixtral for PTQ in NeMo 2.0.~~ done in https://github.com/NVIDIA/NeMo/pull/11607
* Updating `nvidia-modelopt=0.21.0`

**Collection**: LLM / NLP

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# Additional Information
* Related to https://github.com/NVIDIA/NeMo/pull/11607
