opal-rust v2.0.2-2

Added

• First public release of the Rust binding. Binds opal 2.0.2.
• The opal crate compiles vendored C11 sources from vendor/opal/. There is no
  bindgen step. Set OPAL_SRC to compile a local checkout instead. The crate sets
  links = "opal" and is no_std plus alloc.
• Opal, Channel, Operator, and WriteBuf are hand-mirrored as #[repr(C)]
  with snake_case field names. Tests check every size and field offset against the
  C compiler.
• Methods for the eight C functions: new, set_sample_rate, write_reg,
  write_reg_buffered, flush_write_buf, pan, sample, and read_status.
  boxed heap-allocates the ~70 KiB state. write_regs and write_regs_buffered
  take iterator batches. render and render_stereo fill interleaved or typed
  stereo buffers.
• EnvelopeStage and ChannelType transparent newtypes (Display, From<c_int>).
  Index sentinels OP_NONE, MOD_OWN_FB, and CH_NONE. Status bit constants.
  modulator_slot and carrier_slot match the upstream header table.
• VERSION_MAJOR, VERSION_MINOR, VERSION_PATCH, and packed VERSION
  (major * 10000 + minor * 100 + patch), matching OPAL_VERSION_* in opal.h.
• Public sample-rate arguments are u32 hertz. A rate of 0 becomes the native
  OPL3 rate. Values that do not fit in a C int are clamped.
• Edition 2024. MSRV is current stable (1.97).
• NEW (register 105h bit 0) is a live mode bit. Bank 1, waveforms 4-7, CHA and
  CHB, and four-operator pairing apply only while it is set.
• pair_index is the physical partner, or CH_NONE if the channel cannot pair.
  chan_type says whether 4-op is active.
• After Opal::new, every operator's eg_out is 0x1FF.
• A masked timer overflow sets FT1 or FT2. IRQ (bit 7) is set only when that
  timer is unmasked.
• Demo: cargo run --example demo writes a short FM arpeggio to opal-demo.wav.
• Tests cover silence after init, pair-index wiring, NEW as a live mode bit, tone
  generation, save-state clones, buffered write equivalence, resampler full-scale
  step regression, pan, stereo render parity, timer flags, and sample-rate
  round-trip (0 and overflow clamp).