docs: update GPTBigCode model card with standardized usage section

[FrankDannie]

What does this PR do?

This PR updates the GPTBigCode model card to a standardized format compatible with Hugging Face Hub interactive docs.

Changes include:

• Added / blocks for structured usage examples:
  • Pipeline (quick start)
  • AutoModel / AutoTokenizer (recommended for control)
  • Quantization (BitsAndBytes 4-bit example)
  • AttentionMaskVisualizer
  • FlashAttention 2
• Consolidated all usage code snippets for copy-paste usability.
• Preserved notes on model optimizations, expected speedups, and attention implementation.
• Improves readability and makes the docs interactive for users exploring model examples.

This ensures users can quickly experiment with GPTBigCode checkpoints as described in #36979,.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

[Rocketknight1]

cc @stevhliu

[stevhliu]

Thank you so much for the time and effort you put into this—I really appreciate it. With the number of models in Transformers growing so quickly, I’ve been looking into ways to automate model card generation to keep up with the pace. For now, I’ll be closing this PR, but I’m very grateful for your interest in this project!

Thanks again 🤗