Looks good to me. Thanks for adding this. Couple of suggestions:

Fix the format for the default .env.example included in the repo. If someone doesn't want to include the optional variables, it would throw an error by default. Just adding an = sign would fix the problem.

ANKISYNCD_FULL_SYNC_MANAGER=
ANKISYNCD_SESSION_MANAGER=
ANKISYNCD_USER_MANAGER=
ANKISYNCD_COLLECTION_WRAPPER=

Also, you should add instructions to run the tests in the readme. Something like this

mv .config/.env.example .config/.env.local
make init
poetry run make tests

That's a good point. I'm made the changes as requested. Let me know what you think.

Looks good. Thanks for these changes!