Improve debugability of deepcopy errors #1119

Job	Run time
Run tests (3.8)	1m 59s
Run tests on legacy versions (3.7)	2m 16s
Run tests (3.9)	2m 2s
Run tests (3.10)	2m 8s
Run tests (3.11)	2m 7s
Run linters (flake8)	1m 41s
Run linters (pydocstyle)	1m 47s
Run tests (3.12)	2m 8s
Run tests with coverage	3m 1s
Run tests (3.13)	2m 13s
Run linters (mypy)	1m 58s
Run linters (pylint)	1m 57s
Run tests with different pydantic versions	3m 37s
	28m 54s

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