feat: support subdirectory in addon key

[andersmmg]

Fixes #201

[wlsnmrk]

Thanks, this looks great! Would you be willing to add a test (in GodotEnv.Tests) to verify that the subdirectory creation works as expected?

[andersmmg]

I'll look into that, good point!

[andersmmg]

I updated the tests and they all pass, lmk if any changes are needed

[jolexxa]

Thank you! 🙏

I'm always a little scared to merge anything that touches addon resolution, but I suspect this will not break the existing addon dependency system, especially if you have tested locally and confirmed that it will re-install an addon in a subdirectory on top of itself by clearing it out and re-copying it.