Fix typos: accumulation, mismatch, formatting, externally

[arJ-V]

Fix typos

This PR fixes the following typos:

• spelling of "accumulation" in a TODO comment in examples/lora.py (was "accumenlation").
• spelling of "mismatch" in a comment about cache slicing in gemma/gm/text/_prefill.py (was "missmatch").
• spelling of "formatting" in a comment about development dependencies in pyproject.toml (was "formating").
• spelling of "externally-published" in a comment about Google's style guide in .pylintrc (was "externaly-published").