use weekly slots, update nix envs, ics->icalendar

.gitignore

default.nix

flake.lock

flake.nix

lflex_celcat_survival/__init__.py

lflex_celcat_survival/auth.py

lflex_celcat_survival/cmd/fetch_celcat.py

lflex_celcat_survival/events.py

lflex_celcat_survival/ics.py

lflex_celcat_survival/slot_parse.py

pyproject.toml