Enable basic type checking

[qartik]

With my PR #37 I presumed there was some basic type checking in place in the development branch, turns out I was mistaken.

It will be nice to enable it using mypy starting with the default config.

I'm happy to work on it in spare time.

Have a WIP PR at #41.

[qciaran]

Yeah, I would like to eventually to start adding mypy and stricter types. I would be curious to learn how these types are being used/affect pytket-phir.

FYI, I am considering changing some of the typing for the inputs to HybridEngine to use classes that inherit from typing.Protocol because all I really want is duck typing there and not to enforce an ABC. However, I am not super familiar with it, but it seems to fit my intent more (to allow users to supply anything that supports a certain interface).

[qciaran]

Also, FYI, the Generic* classes are not meant to serve as base types but to be a generic example of the ABCs.