[ClausValcaTD]

This PR resolves a critical data loss bug in header_remover.dart where in-place header removal (e.g. outputDir omitted/null and backup: false) opened the target file with FileMode.write while reading from it, truncating the file to 0 bytes.

Changes:

1. Updated removeHeader to write cleaned bytes to a temporary file ($cleanPath.tmp) first.
2. Ensured stream handles are closed before replacing the target file using renameSync with copySync fallback.
3. Added try-finally cleanup logic to delete the temporary file if an exception occurs during execution.
4. Added unit test in core/test/header_remover_test.dart verifying in-place header removal with backup: false on a dummy ROM.

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PR created automatically by Jules for task 3235125612171155444 started by @ClausValcaTD

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