* [CHORE] update mypy and new issues
lnbits/cache.py:21: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs [annotation-unchecked]
lnbits/extension_manager.py:210: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs [annotation-unchecked]
lnbits/db.py:110: error: Only instance methods can be decorated with @property [misc]
lnbits/tasks.py:152: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs [annotation-unchecked]
lnbits/tasks.py:171: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs [annotation-unchecked]
lnbits/core/services.py:520: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs [annotation-unchecked]
lnbits/app.py:520: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs [annotation-unchecked]
lnbits/app.py:525: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs [annotation-unchecked]
lnbits/app.py:532: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs [annotation-unchecked]
* fix db.py
* fix mypy notes, type were not needed
* add simple caching utility
* test cache
* remove prefix, default on get
* check expiry in pop aswell
* remove unnecessary type
* improve invalidation task
increase default interval to 10 seconds - doesnt have to check that often.
instead of recreating the dict everytime mutate the existing one
