Disable distopt contiguous param buffer by default
# What does this PR do ?

This fixes a bug reported by @wdykas, where https://github.com/NVIDIA/NeMo/pull/5684 significantly increased the size of GPT checkpoints.

I think this is because this PR configures the model parameters so they are all views into a single large buffer. However, PyTorch tensors save their underlying memory buffer when pickled, so checkpointing the model results in multiple redundant copies of all the parameters. This PR disables this behavior by default, at the expense of adding an extra copy after each param all-gather.

**Collection**: NLP

# Changelog 
- Disable distopt contiguous param buffer by default.

# Usage
This fix is applied by default. To restore the old behavior, configure the optimizer with `contiguous_param_buffer=True`.

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**PR Type**:
- [ ] New Feature
- [x] Bugfix
- [ ] Documentation

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## Who can review?

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[Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md) contains specific people who can review PRs to various areas.

Pinging @wdykas.

# Additional Information
* Fixes bug from https://github.com/NVIDIA/NeMo/pull/5684.
