add an -inplace option?

I think it would be useful to add an `--inplace` option where the target destination file is the source file :)

Look at the main command-line parsing and file handling logic in the project, likely in a main.go or cmd/ directory. Understand how source and destination files are currently processed. The change involves adding a flag that, when set, makes the output overwrite the input file. Check for existing tests related to CLI flags and file operations to see how to add a test for the new behavior.

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