perf: defer optional typing imports #1154

Job	Run time
Wait for quality and unit checks	2m 37s
Detect matrix mode	8s
Build MyPyC wheels (ubuntu-latest py3.12)	15m 2s
Build source distribution	16s
Build standard pure Python wheel	17s
Test ubuntu-latest py3.12	17s
Verify package integrity	7s
	18m 44s

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