improve the typehint of model.find, to catch a typo where a param is a set instead of dict

[antont]

Had a bug with this kind of typo, it failed silently:

'id': {"==": my_id},
'some_value': {">=", condition_value} #has , instead of :

This makes the linter catch it.

I guess it could be caught and reported at runtime too, additionally.