Implement MLSD & fix MLST

[procr1337]

Disclaimer: A lot of this code was written with AI assistance. I reviewed it & improved the test coverage.

Additional fixes (in separate commits which can be cherry-picked if needed):

1. MLST output was incorrect/out of spec. Output was something like 213 <facts> filename, where it should be a multi-line format initiated by 250- and ended by 250 , as per https://datatracker.ietf.org/doc/html/rfc3659#section-7.2
2. There was a small bug where uid was used instead of gid for MLST facts
3. As noted correclty by @LLeny, facts list must be terminated by semicolon. Grammar from RFC: facts = 1*( fact ";" )

Since async_ftp does not support MLST nor MLSD, we (Claude and me :) added manual TCP-based tests for both commands in the existing sbe-fs integration test suite. This is obviously weaker since we don't have a compliant client to check against. In addition, I manually tested this against rclone's FTP client and FileZilla.

[LLeny]

Small issue, I believe the rfc states that all facts must end with a ';', even the last one. It's problematic with the rclone ftp implementation.

[procr1337]

@LLeny you are absolutely right, thank you! I didn't encounter any issues in my testing with rclone however

[LLeny]

@procr1337 For reference, I did, there: https://github.com/LLeny/proton-drive-bridge/issues/9

[hannesdejager]

Thank you @procr1337 and @LLeny