Publish eval2otel-python to PyPI

[haasonsaas]

Summary

PR #43 and PR #44 added the Python SDK preview, optional OTLP emission, provider auto-instrumentation hooks, an opentelemetry_instrumentor entry point, and optional Pydantic validation. The remaining release task from #2 is to publish the Python package as its own PyPI artifact.

What to do

• Decide the package name and ownership for eval2otel-python on PyPI.
• Configure PyPI trusted publishing or a scoped API token for this repository.
• Add a release workflow that builds python/ into sdist/wheel artifacts and publishes them on GitHub release.
• Add a release smoke that installs from PyPI and imports Eval2Otel, instrument_all, and Eval2OtelInstrumentor.

Acceptance criteria

• A GitHub release publishes the npm package and the Python package without manual local steps.
• pip install eval2otel-python works from a clean environment.
• The installed package exposes the opentelemetry_instrumentor entry point named eval2otel.
• The release docs explain npm vs PyPI versioning expectations.

Split from #2 after the SDK implementation landed in #43 and #44.