style: unified headers extensions convention across the repo

[SomePersonFromMars]

Closes #

⚠️ Breaking changes ⚠️

• None for the public JS/TS API.
• Internal C++ include paths change for a handful of renamed headers (.h ↔ .hpp). This only affects code that includes those headers directly.

Introduced changes

• Adopt a consistent C++ header extension convention in common/cpp/audioapi/:
  • .hpp — header-only templates (class or function)
  • .h — non-template code (usually paired with a .cpp)
• Renamed headers to match the convention:
  • .h → .hpp: CompositeAudioParam, RuntimeInstanceCache, AudioEventPayloadMapping, TypedAudioNodePtr
  • .hpp → .h: AudioUtils, ParamRenderEventFactory
• Updated all affected #include paths across the native engine, tests, and worklets package.
• Documented the convention in build-compilation-dependencies and updated related skill references (audio-nodes, utilities, thread-safety-itc).

Checklist

• Linked relevant issue
• Updated relevant documentation
• Added/Conducted relevant tests
• Performed self-review of the code
• Updated Web Audio API coverage
• Added support for web
• Updated old arch android spec file

[closetcaiman]

nice!

it's always good to have these things sorted out!!