Fix SevenZip::reset() to also reset formatFlags

[insign]

This PR addresses a bug where SevenZip::reset() failed to reset $this->formatFlags.

When reset() was called, it correctly cleared $this->format (so that getFormat() would return the default '7z'), but left $this->formatFlags unchanged. As a result, subsequent operations would attempt to build a '7z' archive but use compression flags from the previously configured format (e.g., -tzip), causing 7-Zip executions to fail with invalid archive errors.

The fix calls setFormatFlags() inside the reset() method to ensure flags correctly align with the reset format. A test case was also added to ensure this behavior is verified in the suite. No .md files were changed as none were impacted by this fix. All pre-commit checks pass and no dummy test files are leaked.

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PR created automatically by Jules for task 2340808107410579736 started by @insign

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