Rewrite it in Rust

[Antti]

Summary

This PR rewrites audiowaveform in Rust and removes the legacy C++/CMake implementation from this repository.

The repo is now centered on a Rust workspace with:

• crates/audiowaveform: reusable library crate
• crates/audiowaveform-cli: thin CLI wrapper

It also updates the repository metadata to reflect that this is the canonical FetLife-hosted Rust rewrite of the original BBC project.

Changes

• Added a first-class Rust library for:

  • audio decoding with Symphonia
  • raw PCM parsing
  • waveform generation and resampling
  • waveform .dat / .json / .txt serialization
  • PNG rendering
  • PCM16 WAV transcoding

• Added a Rust CLI that keeps the familiar audiowaveform command shape while using typed clap enums and styled help output.

• Expanded the Rust test suite to cover:

  • decode/generate flows
  • waveform I/O and validation
  • PNG rendering
  • WAV transcoding
  • CLI smoke/regression cases

• Consolidated fixtures into a single fixtures/ directory.

• Removed legacy project infrastructure:

  • C++ source and tests
  • CMake build files
  • distro packaging files
  • old CMake-based GitHub Actions workflow

• Updated docs and metadata:

  • README now points to https://github.com/fetlife/audiowaveform
  • original BBC project is linked and credited
  • changelog now clarifies that older entries are inherited history
  • CI and CodeQL now target the Rust workspace

Notes

• Opus remains intentionally unsupported in the Rust implementation for now.
• Some Rust fixture outputs are intentionally Rust-owned goldens where decoder/renderer behavior does not byte-match the legacy stack.

Validation

cargo fmt --all
cargo test --workspace
cargo check --workspace --examples
cargo check --workspace --quiet