Improve debugability of deepcopy errors #1114

Job	Run time
Run tests on legacy versions (3.7)	2m 12s
Run tests with different pydantic versions	3m 58s
Run tests (3.8)	2m 1s
Run tests with coverage	3m 14s
Run tests (3.9)	2m 11s
Run tests (3.10)	1m 56s
Run linters (flake8)	1m 47s
Run tests (3.11)	2m 7s
Run linters (pydocstyle)	1m 58s
Run tests (3.12)	2m 12s
Run linters (mypy)	1m 52s
Run tests (3.13)	2m 11s
Run linters (pylint)	1m 55s
	29m 34s

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