This commit adds mypy annotations for both the main
bots and the bots testing runner. It involves a change
to the BotHandlerApi send_message and update_message
funtions, which is compatible with every bot.
Tweaked by tabbott to use more expressive annotations.
This test uses unittest and mock library. It mocks
'BotHandlerApi' class. This test works independent of
the rest of the code outside contrib_bots folder.
Merged with a few changes by tabbott to fix lint issues; we'll need to
do further work on this framework, but since it's not hooked up to
anything, it's reasonable to merge early so others can collaborate on
improving it.