Typos in mutliple files

Following are the typo listed:

- 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").

I have raised a pr for fixing this. Have a great day!