Type hint improvements

[MarquessV]

Some fixes and improvements influenced by resolving some mypy issues in pyQuil#1566.

[MarquessV]

This fixes an issue where mypy would expect a sub class to return an instance of itself even when leaning on it's parent class for initialization. For exampe:

class Base:
    def __new__(cls) -> "Base": ...

class Sub(Base):
    def __new__(cls) -> "Sub":
        return super().__new__(cls)  # mypy complains that the function should return `Sub` but it returns `Base`

The above is valid code, an instance of Sub() would work as you would expect Sub to work, and calling super().__new__ to initialize a subclass is what the Python docs recommend.

The Self type is essentially a shortcut for a generic TypeVar bounded by the parent class, meaning that a return type of Self can be used in a child class without violating any type rules.

[MarquessV]

Accepting Sequence instead of List makes these type hints more flexible. A List is a Sequence, and pyo3 converts Sequences to Rust Vecs, so this doesn't betray the reality of the bindings.