Preserve QuickTime v2 audio sample entries

[kixelated]

Summary

• expose and preserve QuickTime audio sample entry versions and their version-specific fields
• decode version 2 sample rates and channel counts from the authoritative extension fields
• represent sample rates as f64 and channel counts as u32, while validating the narrower version 0/1 encoding limits
• retain version 2 entries when re-encoding instead of emitting a version 0-shaped entry with placeholder values

Root cause

Version 2 entries put placeholder values in the legacy prefix (3 channels and 1 Hz). The decoder read the authoritative f64 sample rate and u32 channel count from the version 2 extension but discarded them. Encoding then always emitted a version 0 entry, so decoded version 2 audio could be re-encoded with the placeholders as real values.

Impact

High-rate and QuickTime PCM audio now reports its actual rate and channel count, including rates above 65535 Hz, and round-trips without losing the version 2 layout.

Validation

• cargo test --all-targets --all-features
• cargo clippy --all-targets --all-features -- -D warnings
• cargo fmt --all -- --check
• git diff --check

Closes #195

[kixelated]

IDK if I care enough about QuickTime?