Fix slotted reference cycles on 3.14 #1600

Job	Run time
Check types using pyright	13s
Build & verify package	17s
Verify dev env	12s
Run doctests & render changelog	13s
Tests & Mypy on 3.9	38s
Tests on pypy-3.10	17s
Tests & Mypy on 3.10	1m 18s
Tests & Mypy on 3.14	3m 2s
Tests & Mypy on 3.13	1m 4s
Tests & Mypy on 3.11	1m 3s
Tests & Mypy on 3.12	1m 10s
Combine & check coverage	9s
required-checks-pass	3s
	9m 39s

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