Fix WavPack sample shift

[sbooth]

For lossless decoding

[Copilot]

Pull request overview

Fixes WavPack lossless sample shifting for non-byte-aligned bit depths by shifting based on bytes-per-sample rather than bits-per-sample. WavPack delivers samples low-aligned within the bytes used for the original data (e.g. 20-bit samples occupy 3 bytes), so shifting by 32 - bitsPerSample over-shifts and corrupts the high-aligned 32-bit output expected by the processing format.

Changes:

• Replaced 32 - bitsPerSample with 32 - 8 * WavpackGetBytesPerSample(_wpc) in the lossless decode path.
• Expanded the explanatory comment to clarify WavPack's low-alignment-within-byte-boundary behavior.

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