Include C-API shared library in release bundles #25

The prebuilt release bundles only ship parakeet-cli. Would be great to also include the C-API shared library and header:

• parakeet.dll (Windows) / libparakeet.so (Linux) / libparakeet.dylib (macOS)
• parakeet_capi.h

This would enable direct integration via ctypes/dlopen without compiling from source. The C-API is already in the repo and actively maintained.
CI change: add -DPARAKEET_SHARED=ON and include the outputs in the package step.

Thanks for the great work!