pydevd: add build-pydevd.yml for riscv64 wheels

[luhenry]

• Package: pydevd
• Version: 3.5.0
• Source: https://github.com/fabioz/PyDev.Debugger/
• Docs: https://github.com/fabioz/PyDev.Debugger/

Compiles pydevd's Cython frame-tracing extensions (pydevd_cython, _pydevd_sys_monitoring_cython) that back the PyDev/PyCharm/VS Code Python debugger's hot path. Upstream publishes no riscv64 wheel.

Mirrors upstream's pydevd-release-manylinux.yml.

Differs from upstream

• Added CIBW_ENVIRONMENT: PIP_EXTRA_INDEX_URL=... - public PyPI ships no riscv64 Cython wheel for before-build's pip install cython.
• Added CIBW_TEST_COMMAND - upstream's release workflow uploads wheels untested; this exercises the built extensions.

Matrix: cp312/cp313/cp314, no cp314t - upstream ships no cp3xxt wheel, its own test matrix has no free-threaded job, and setup.py's classifiers say nothing about free threading.

Testing

• Asserts _pydevd_bundle.pydevd_cython and _pydevd_sys_monitoring._pydevd_sys_monitoring_cython are real .so extensions, then runs the frame-eval, sys-monitoring, tracing, bytecode-manipulation, safe-repr, and thread-info suites from tests_python.

License: Matches upstream's own wheel exactly - only LICENSE-EPL ships; no GPL sources.

CI pending.