release: prepare v0.2.0

[gouyt13]

Summary

• bump the Python package version to 0.2.0
• build and test portable Linux x86-64 wheels for CPython 3.9–3.14
• publish tagged releases to PyPI through Trusted Publishing and attach wheels to GitHub Releases
• redesign the README around installation, adopters, benchmark results, and quick starts
• add the benchmark image to the documentation homepage
• point multi-bit paper references to the SIGMOD camera-ready publication

Verification

• built and installed a local rabitqlib-0.2.0 wheel with native CPU tuning disabled
• Python test suite: 58 passed
• mkdocs build --strict --config-file docs/mkdocs.yml: passed
• README rendered successfully through GitHub's Markdown API
• git diff --check: passed

Release

After this PR is merged, pushing the v0.2.0 tag will build and test the wheels, publish them to PyPI, and create the GitHub Release.