I've corrected some obvious issues, and we can fix others over time.
Mypy tests are currently broken, as adding the type hints has increased
mypy's testing surface.
No need to reorder existing cards, which may have been manually
ordered by the user, when importing notes if we can give cards
a proper due number from the start. Retrieving any sibling's
due number for this is easy as all relevant cards will have
already been queried for when generating the new cards.
If duplicate notes are already in the collection and, based on the first
field of all of them, they should be updated, update all of them instead
of just the first one we come across.
When "allow HTML" was turned off, Anki was replacing newlines with <br>s
in the text of the new notes before it escaped HTML characters, so the
line breaks were becoming <br>.
Even if there are several (duplicate) notes in the collection that
match, only send the message once to avoid making it look like multiple
dupes have been added.
