deflate: add build-deflate.yml for riscv64 wheels

[luhenry]

• Package: deflate
• Version: 0.9.0
• Source: https://github.com/dcwatson/deflate
• Docs: https://github.com/dcwatson/deflate

Python C extension wrapping libdeflate, a fast DEFLATE/zlib/gzip compression and decompression library vendored as a git submodule and statically linked. Upstream publishes no riscv64 wheel.

Mirrors upstream's build.yml.

Differs from upstream

• CIBW_BUILD_FRONTEND: build - upstream's build[uv] crashes cibuildwheel's audit step on the self-hosted riscv64 runner (no host uv).
• Checkout pinned to a commit, not a tag - upstream stopped tagging releases after 0.7.0; the pinned commit's tree is byte-identical to the 0.9.0 sdist.
• Nothing else: libdeflate already ships a generic/RVV riscv64 code path (no x86/arm-only SIMD gate), so no patch is needed.

Matrix: cp312 + cp314t - wheels are abi3 (wheel.py-api = "cp311"), collapsing cp312/cp313/cp314 into one build; cp312 is our floor.

Testing

• same as upstream

License: OK. libdeflate is MIT, same as deflate itself; the wheel ships only the top-level MIT LICENSE, matching upstream's own published wheels.

Matrix cp312/cp314t x manylinux/musllinux; CI running.