v1.8.4

Packaging fixes for downstream consumers (lemonade):

- linux-x64-cpu, linux-x64-vulkan: ship real .tar.gz archives
  (whisper-v1.8.4-linux-{cpu,vulkan}-x86_64.tar.gz) instead of
  .zip-renamed-to-.tar.gz.
- New windows-npu-x64 job produces a flat
  whisper-v1.8.4-windows-npu-x64.zip (no nested zip).
- bindings/java: fix C size_t mapping on Windows x64 (resolves
  intermittent JNA "Invalid memory access" in bindings-java CI).