Make validators optional in deep_mapping (#1448) #1619

Job	Run time
Verify dev env	9s
Check types using pyright	15s
Build & verify package	14s
Tests on pypy-3.10	26s
Tests & Mypy on 3.9	28s
Tests & Mypy on 3.12	1m 7s
Tests & Mypy on 3.11	1m 0s
Tests & Mypy on 3.10	1m 7s
Tests & Mypy on 3.13	1m 8s
Tests & Mypy on 3.14	2m 19s
Run doctests & render changelog	13s
Combine & check coverage	11s
required-checks-pass	3s
	8m 40s

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