Fix the earliest negative correlation offset

[Shubham-Padkonde]

When the strongest match occurs at the earliest negative offset, find_offset_between_buffers reports a positive offset instead. The boundary returned by cross_correlation is exclusive, as also used by the plotting code's range, but the wraparound check uses > rather than >=.

Include that boundary in the negative-offset conversion. A deterministic regression uses matching feature frames and the real standardization/correlation code: it reports +21 frames before the fix and the correct -10 frames afterward.

Validation: all seven tests pass under Linux with FFmpeg, including the existing audio-file and CLI tests. Black and git diff --check pass.

[elvum]

LGTM. @chrisn?

[chrisn]

Thank you for contributing @Shubham-Padkonde. And thank you for reviewing, @elvum.