Upgrade mypy to v1.0 and use `typing.Self`
With the release of mypy 1.0, PEP 673 is supported, meaning the bound TypeVar types used extensively in kilter.protocol.messages can be removed and replaced with typing.Self.
With the release of mypy 1.0, PEP 673 is supported, meaning the bound TypeVar types used extensively in kilter.protocol.messages can be removed and replaced with typing.Self.