Release Testing

There have been repeated examples with releases which pass tests in repo but have resulted in released artifacts to PyPI to and Homebrew with serious problems.
- Refactor the CLI integration tests to allow for optional testing against an external `planemo` command.
- Extend `make release` with some real testing. After publishing to test PyPI:
- Create a temp virtualenv.
- Install all dependencies
- Install planemo from test pypi.
- run release tests.

Start with the CLI integration tests and the make release target. Trace how tests invoke planemo and how release artifacts are published to test PyPI; then define the temporary virtualenv flow, dependency installation, external planemo installation, and release-test execution. Done means release testing exercises the published artifact rather than only the repository code.

Written by the indexing model from the issue text.