unicorn: add build-unicorn.yml for riscv64 wheels

[luhenry]

• Package: unicorn
• Version: 2.1.4
• Source: https://github.com/unicorn-engine/unicorn
• Docs: http://www.unicorn-engine.org

Compiles unicorn's QEMU-TCG-based CPU emulator core via CMake and packages the resulting libunicorn.so behind the ctypes bindings in bindings/python. Upstream publishes no riscv64 wheel.

Mirrors upstream's own build-wheels-publish.yml, narrowed to the Linux manylinux job.

Differs from upstream

• Installs cmake via CIBW_BEFORE_BUILD - setup.py shells out to it directly and it is not a declared build dependency.
• Stages COPYING/COPYING.LGPL2/COPYING_GLIB/AUTHORS.TXT into bindings/python before the build - upstream ships none of them in the wheel, though the source is GPL-2.0/LGPL-2.0.

Matrix: cp312/cp313/cp314 only, one cp37-abi3 build reused across all three; no cp314t, because setup.py sets py_limited_api unconditionally and setuptools raises under Py_GIL_DISABLED, so upstream ships no free-threaded wheel for any platform.

Testing

• same as upstream (tests/regress via unittest discover), with capstone pinned to our registry's 5.0.9 since upstream's capstone==6.0.0a2 test pin has no riscv64 wheel anywhere.

License: Wheel bundles unicorn's own GPL-2.0/LGPL-2.0 core sources (COPYING/COPYING.LGPL2/COPYING_GLIB); upstream ships none of them and its own metadata mislabels the project BSD, so the build copies them into bindings/python before cibuildwheel runs.

Built on cp312; 83 passed, 2 skipped.