[kvlonge]

Why

Fork CI took about 48 minutes, mostly waiting on the TypeScript/WASM SDK build, and each fork release built 32 per-interpreter wheels in about 2 hours. The fork ships only the Rust crate and a CPython 3.12+ Python package.

Changes

• Skip sdk-build and go-sdk outside tobilg/polyglot. Every Rust and Python check still runs.
• Build one stable-ABI (abi3, CPython 3.12+) wheel per platform through an opt-in abi3 feature. The upstream default build is unchanged.
• Set requires-python = ">=3.12".
• Add a build-only release path. It runs on manual dispatch, and on PRs that touch the release workflow or Python package metadata. Publishing still happens only on python-v* tags.
• Linux and macOS smoke tests assert that the wheel is abi3.

Verification

• A local python_release build with --features abi3 produced cp312-abi3. The same wheel passed all 321 Python binding tests on CPython 3.12 and 3.14.
• Paired fresh-process compiles on a downstream project matched the per-version wheel (cold 13.57s vs 13.61s, warm 6.60s vs 6.63s), with byte-identical artifacts in all 12 runs.
• This PR runs the build-only release workflow on all five platforms.