Add audio fixtures and tests for Audio and AcidChunk

[pixelate]

Summary

• Adds test/fixtures/ with 28 audio files covering every combination of sample rate, bit depth, and file type defined in config/devices.yml (WAV, MP3, AIF, AIFF), plus M4A variants for each sample rate/bit depth pair as input format fixtures
• Adds test/wavesync/acid_chunk_test.rb — tests read_bpm and write_bpm round-trips against real WAV fixtures across different rates and bit depths
• Adds test/wavesync/audio_test.rb — tests sample_rate, bit_depth, bpm, write_bpm round-trips, and find_all against real fixture files for all supported formats
• Adds FIXTURES_PATH constant to TestCase, rake and logger gems to Gemfile