docs: fix broken links for FusedGATConv and MoleculeGPT and fix typo

[supawesome]

Hi, my first PR here 👋

Summary

This PR fixes several broken links and a typo across docs and example files:

• Fixed broken links for FusedGATConv and MoleculeGPT in the corresponding .py files
• Fixed broken link for FusedGATConv in README.md
• Added links for MoleculeGPT and GIT-Mol, fixed link for techQA dataset in examples/llm/README.md
• Fixed a typo in the name of ProteinMPNN paper

Verification

• Docs build verified locally (make html)
• All relevant tests passed (pytest -k "not mps")
• Markdown files autoformatted with pre-commit hooks