fix: improve reporting of formatted file contents to LLM

[ezyang]

Stack from ghstack (oldest at bottom):

• -> fix: improve reporting of formatted file contents to LLM #278
• chore: Update project prompt as format is now automatic #277
• fix: make codemcp run work outside project root #276
• feat: integrate autoformatting in WriteFile and EditFile commands #273
• chore: format #274

In the calls to run_formatter_without_commit for WriteFile, we need to be a bit more careful how we report the contents of the edited file back to the LLM. Specifically, we need to say what the file looks like POST-formatting.

f378d7e  (Base revision)
848e33b  Update run_formatter_without_commit to return post-formatting file contents
eb1e368  Update write_file to track post-formatting file contents
e76eefa  Update edit_file to track post-formatting file contents
f6bcb3b  Update edit_file to show post-formatting content in snippets
4335196  Update write_file to show post-formatting content snippets
e184154  Clarify that edit_file snippets show post-formatting content
0f41905  Import async_open_text for asynchronous file operations
HEAD     Use async_open_text instead of blocking open() for file reading

codemcp-id: 283-fix-improve-reporting-of-formatted-file-contents-t