Various typing/`dataclasses` fixes #704

Job	Run time
Typos	4s
Pylint	50s
Documentation	41s
Tests for downstream project loopy	3m 59s
Mypy	24s
Pytest on Py3.8	31s
Tests for downstream project pytential	44m 40s
Tests for downstream project pytato	6m 9s
Pytest on Py3.9	30s
Ruff	5s
Pytest on Py3.x	38s
	58m 31s

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