rbt patch now has type hints all throughout. This helped catch some

places where we were mixing types, leading to crashes. Notably, JSON

output would crash when dealing with conflicting files represented as

Unicode strings (which are expectd due to the type hints) rather than

byte strings.
It now uses the Patch class to track patches to apply, wrapped by a

small PendingPatchInfo dictionary with the rest of the information

that it needs to track.
This is in preparation for using new patching logic for more SCM-driven

patch application, which is in development now.
As a note, the Patch command has been renamed to PatchCommand, to

avoid conflicts with the Patch class. This will require those using

the development tree to re-run pip install -e . to register the new

entrypoint.