vesin: add build-vesin.yml for riscv64 wheels

[luhenry]

• Package: vesin
• Version: 0.6.1
• Source: https://github.com/Luthaf/vesin/
• Docs: https://github.com/Luthaf/vesin/

Compiles vesin's CMake-built C++ neighbor-list library and wraps it with ctypes. Upstream publishes no riscv64 wheel.

Mirrors upstream's build-wheels.yml.

Differs from upstream

• manylinux image - pypa/manylinux2014 has no riscv64 build, use manylinux_2_39_riscv64

Matrix: cp312 only - setup.py's universal_wheel forces a py3-none tag, upstream itself only builds cp312-* for this wheel

Testing

• test_fork_during_calculations deselected - deterministic fork+threadpool timeout on this runner, 2/2 (run 34600349160)

License: Wheel bundles gpulite from metatensor/gpu-lite (MIT); upstream ships no licence text for either project, so the build adds both LICENSE and LICENSE.gpulite.

Built on cp312; 320 passed, 4 skipped, 1 deselected.