Run e2e test with published libs

[robertschonfeld]

To prevent an issue like #147, we should run e2e tests with libs published to pypi i.e. pip install ...

Occasionally we can also run against multiple recent versions.

Most of all run python tests either
- using maturin build --release
- against the final build downloaded from PyPi (at least a smaller smoke test)

Also consider pinning the maturin action version in publish_python.yml.

We can also discuss using github releases/tags as triggers for the publishing.

[jerguslejko]

• [py] pin maturin version
• [ci] run publish workflow on tag event (unrelated but nice for maintainers)

this one is WIP. the gh pipeline needs tweaking to run the tests correctly

• [ci] run tests after building python wheels

[jerguslejko]

using maturin build --release

this one I don't think would reveal anything since the --release flag only tells rustc to optimize the code. there should be no difference in behaviour whatsoever (modulo standard stuff)