The macOS job finally reached the build (after the vcpkg manifest fix) and
hit a macOS-only compile error in the VideoToolbox import: `*ptr as
*const T` parses as `(*ptr) as *const T`, so `sw_format` was read off a
pointer instead of the AVHWFramesContext. Bind the frames pointer first.
Also fix the warnings the cross-check surfaced: the redundant
MTLPixelFormat import, and doc comments on an extern block and a
thread_local! (rustdoc does not document those).
Verified locally with a host-cc wrapper:
`cargo check -p oak-core -p oak-codec -p oak-node -p oak-render
-p oak-task -p oak-plugin --target aarch64-apple-darwin` is clean.
(oak-app itself needs a real Apple toolchain for ring.)
Mike-Solar
13ddd8c0e7