Add type hints to the circuit module

[BoxiLi]

• Add type hints to the circuit module
• Rename texrenderer.py to tex_renderer.py
• Remove circuit.adjacent_gate as it is replaced by to_chain_structure long ago.

[hodgestar]

What Python versions do we need to support? If 3.9+ should we do from __future__ import annotations and then not have to import so many things from typing? E.g. Optional[Union[int, List[int]] becomes int | list[int] | None.