typing: disable a few incorrect warnings in pywatchman The module-attr warnings are for things that only exist on Windows, and the wrong-keyword-args warning is due to a special case for a specific constructor. Both of these are properly conditionalized.

watchman: refactor transport connecting to unconfuse pytype Pytype sees `self.proc` as potentially `None` here, even though it's set by the `_connect()` logic. Instead of asserting, simply use the process returned by that method (which it sets into `self.proc` before returning, so there's no functional change here).

watchman: refactor `ctypes.windll.kernel32` references to a local variable This is flagged by pytype as an attribute-error, and it's easier to disable that in a single place.

typing: disable [unsupported-operands] warning in the largefiles outgoing hook For some reason, pytype thinks `toupload` is a set: No attribute '__setitem__' on Set[nothing] (It actually is a set in the subsequent `else` branch, but I'm not interested in trying to rewrite this to be consistent.)

typing: add some assertions that a variable isn't None In the case of blackbox, there's a default limit if one isn't explicitly supplied. For the monotone regex, neither group is optional, so a match means it's not None.

largefiles: reference `mercurial.configitems.dynamicdefault` directly Pytype was unable to see `dynamicdefault` on `eh.configitem`. This is clearer anyway.

releasenotes: fix a typo in a comment

schemes: fix a broken check for drive letter conflicts Flagged by pytype locally. It appears to have regressed in 1863584f2fba (not yet released). This seems like an obvious typo- `dict.isalpha()` is nonsense. There's no crash though because `schemes` is pre-populated with 5 schemes (that are all now defunct), so the length of the dict is never 1, so it's impossible to abort.