### Integer decoders — fast kernels that keep every output integer

- `wai-rs` adds `int_kernels`: register-blocked convolution, transposed
  convolution and IGDN kernels (NEON widening multiply-accumulate on aarch64,
  portable Rust elsewhere), scoped worker threads (none on wasm), and a run-time
  `Policy` that selects them or the retained scalar reference kernels. The
  int_synth, int_hyper, int_audio, int_splat, int_world and JPEG-AI synthesis
  decoders dispatch to them. No bitstream, conformance vector or hash changes.
- The claim, precisely: for every input the reference decodes, every policy
  returns the same integer for every output element; with overflow checks on, a
  fast policy panics on the inputs where the reference panics, though the panic
  message can differ. Geometry the fast path does not handle, including a
  transposed convolution whose sizes the reference's own arithmetic cannot form,
  goes to the reference. The fast path's own allocations and loops stay in
  proportion to what the reference reads and writes, whatever the stride or
  padding. The two paths still allocate different buffers, so an allocation that
  fails is outside the claim. It is argued by construction and tested, not
  machine-proved. The rules, the tests, their limits and the measured throughput
  (one machine) are in
  [`research/decode-throughput.md`](research/decode-throughput.md).
- CI: `wai-conformance` runs the kernel-equivalence tests, every committed
  vector that reaches the kernels and edge geometry through the public decoders
  (strides up to `usize::MAX`, padding far beyond the kernel, and strides and
  paddings at which the reference's size arithmetic overflows), under every
  policy, with overflow checks on and off, on each platform leg. Geometry on
  either side of the padded-input bound is pinned too: at the bound the fast
  kernel runs, beyond it the reference does, and a test-build count of
  fast-kernel entries shows which one ran.
  `wai-byte-equality` and `wai-formal-verification` fire on changes to
  `int_kernels.rs`.

