feat(riff): add RF64/BW64 format support

[tphakala]

Summary

Adds RF64/BW64 format support to the WAV demuxer, enabling playback of audio files exceeding the 4GB RIFF size limit.

• DS64 chunk parser — parses 64-bit sizes (riff_size, data_size, sample_count) and table entries per EBU Tech 3306
• RF64 detection — recognizes RF64 stream marker alongside standard RIFF
• 64-bit size handling — uses ds64 values only when the 32-bit sentinel (0xFFFFFFFF) is present, per spec
• Probe/scoring — adds RF64 probe descriptor and accepts RF64 marker in format scoring
• Overflow safety — validated ds64 table bounds, checked arithmetic for data position calculations
• Tests — ds64 parsing unit tests + RF64 integration tests (small files, >4GB metadata, fallback, ds64-in-standard-WAV ignored, malformed table rejection)

EBU Tech 3306 compliance

• DS64 values only override 32-bit fields when those fields are set to -1 (sentinel)
• DS64 sample_count takes precedence over fact chunk and computed value for RF64 files
• Table entry count validated against declared chunk size

Context

Fresh rewrite of #425 for dev-0.6 as requested. The original PR targeted master but a mechanical rebase failed due to significant API changes in dev-0.6 (lifetimes on WavReader, FormatInfo/MetadataInfo constants, Track construction, DataChunk.len as Option<u32>, etc).

Test plan

• cargo check -p symphonia-format-riff (all platforms)
• cargo test -p symphonia-format-riff (11/11 pass)
• cargo clippy -p symphonia-format-riff (clean)

Note: Rustfmt CI may fail due to pre-existing formatting issues in aiff/mod.rs and fix_wave_channel_mask on the dev-0.6 branch — unrelated to this change.