Base expression node types on `dataclasses` #630

Job	Run time
Pytest on Py3.8	28s
Pytest on Py3.9	32s
Pylint	56s
Pytest on Py3.x	37s
Documentation	37s
Tests for downstream project loopy	5m 41s
Tests for downstream project pytential	21m 22s
Ruff	5s
Tests for downstream project pytato	8m 19s
	38m 37s

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