[High Prio] Implement a reusable binary solution for tests using `tox` and w/o

[symonk]

Right now we have some major problems in terms of tox/testing. Everything works fine from a normal perspective after a simple playwright install because browsers reside in ~/.cache/ms-playwright/* - however, in tox this is a pytes tmpdir, which would auto acquire binaries pretty much on every run.

Implement some sort of solution for development that allows tox to leverage / reuse existing binaries. This is also slightly tricker because pytester (probably) doesn't always pass the ENV through etc.