Prepare v0.3.0 release

[polishdataengineer]

What changed

• bump the package, runtime fallback, and lockfile from 0.2.1 to 0.3.0
• move the adaptive scheduling and benchmark-tooling changes from Unreleased into the 0.3.0 changelog section
• update current-version documentation, benchmark output names, and the real-project manifest example
• regenerate the benchmark page and both complete LLM references

Why

This prepares the adaptive scheduling, testenix tune / testenix benchmark, opt-in safe module sharding, trusted collection manifests, and provenance-gated benchmark tooling already merged into main for a public minor release.

Historical benchmark evidence remains explicitly labelled as Testenix 0.1.0. This release does not claim that the historical 3.15× synthetic result applies to 0.3.0 or to real projects.

Validation

• 461 tests passed with direct pytest
• 461 tests passed through testenix pytest
• Ruff check and format check
• mypy and pyright
• generated documentation asset check
• Sphinx warning-as-error build
• wheel and sdist build as testenix-0.3.0
• Twine strict validation and wheel-content validation
• isolated wheel and sdist version/run smoke tests
• pytest 9.1.1 and pytest 8.3.0 compatibility smoke tests
• multi-agent release, documentation, metadata, and workflow audits: no remaining blockers

Release procedure

After this PR is green and merged, create a public, non-prerelease GitHub Release with tag v0.3.0 targeting the exact merge commit on main. The release workflow will rebuild and verify the distributions, then publish them to PyPI through Trusted Publishing after approval of the protected pypi environment.