feat: add cjdk to allow it all to work without any java or maven installed

[tlambert03]

This PR attempts to allow pip install bffile (or whatever we call it), to Just Work® even if java and maven is not installed on the system. An explanation of how this works is added to the readme here

Tests are added to test that we work both with a system installed java (via actions/setup-java) as well as a cjdk-installed version (when java-version = ''). This also adds a test on bioformats-version 6.0.1

The autoused cache_dirs fixture in conftest.py ensures that tests don't have side effects: both that they don't unexpectedly pass due to a resource found in the testers environment, or leave any residual files on the testers user space. (unless opted into with --allow-cache to speed it all up)

@ctrueden, would be great if you could have a look at this when you have a moment (and @marktsuchida... if you want to verify my usage of cjdk)

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[tlambert03]

this work was upstreamed to scyjava in scijava/scyjava#80