Add native voice dependency build recipe

[copyberry]

Add native voice dependency build recipe

Why

The pinned voice source inputs can be prepared but do not yet provide compiled
native libraries for downstream integration.

What changed

• Add build_native.py to build a shared-library prefix for the supported voice
  dependencies on native x64 and ARM64 GNU/Linux, macOS, and Windows MSVC hosts.
• Require explicit toolchain inputs, isolate dependency discovery to the output
  prefix, and record command logs and build state for provenance and failures.
• Expose the recipe and source inputs through //third_party/voice:build_inputs
  and document its prerequisites, outputs, and integration boundaries.

Testing

• PYTHONSAFEPATH=1 python3 -m unittest discover -s third_party/voice -p 'test_build_native.py'

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