silently discard trailing partial sample byte

[JaySon-Huang]

Problem

close #63, close #81

WavReader::new() currently rejects WAV files where data_len % bytes_per_sample != 0, returning an Error::FormatError ("data chunk length is not a multiple of sample size").

However, real-world audio files often have a missing final byte from truncated transfers, and mainstream players (VLC, ffmpeg, Symphonia) handle them gracefully by ignoring the trailing byte(s).

Why the change is safe

• num_samples is computed via integer division, which naturally discards the partial trailing sample.
• WavReader only uses num_samples for subsequent reads — the truncated data_len is never referenced again.

Verification

Tested against 7 real-world truncated WAV files that previously failed:

• 6 files from a legacy game asset collection (16-bit mono, 22050 Hz)
• 1 file from hound issue hound errors out when trying to read samples from this file #81 (16-bit mono, 24000 Hz)

All 7 files now decode successfully with the patch, producing the expected sample counts (last partial sample silently dropped). 88 non-truncated control files continue to decode identically.