Read FLAC as well as WAV, behind one reader that dispatches on content

[ephemer]

AudioFileReader is a Sequence over either container, chosen by inspecting the file's contents rather than trusting its extension, so callers that only want samples stop caring which format they were handed. FlacReader decodes through a vendored dr_flac in a new CDrFlac target; the audio-file-compare executable exists to diff the two readers over the same material.

Based on memory-map-slice (0bd273c), which is the branch AudioToMIDI-Training pins, so merging here moves that pin with no manifest change.

Why this is needed downstream

AudioToMIDI-Training already calls AudioFileReader from Dataset.swift, EntryPoint+Transcription.swift and MelSegments.swift. Those call sites cannot compile against the pinned revision, and the failure is confusing rather than obvious: swift package edit records the edit in .build/workspace-state.json, but xcodebuild reads its own .build/xcode/SourcePackages/workspace-state.json, which still says sourceControlCheckout. So xcodebuild silently compiles the pinned checkout and reports cannot find 'AudioFileReader' in scope while the type sits right there in the working tree.

Verification

• swift build clean.
• swift test: 10/10 pass, including 9 AudioFileReaderTests covering content-based dispatch, slice repeatability, and the FLAC fixtures in Tests/Flacs.

Contents

Sources/WavReader/AudioFileReader.swift	the dispatching reader
Sources/WavReader/FlacReader.swift	FLAC decode path
Sources/CDrFlac/	vendored dr_flac (528 K, 3 files)
Sources/AudioFileCompare/	audio-file-compare diff tool
Tests/Flacs/	4 FLAC fixtures (224 K)
Package.swift	+17 lines for the new targets

[ephemer]

FYI @reckjn