fix memory leak with recursive definitions creating reference cycles #4101

Job	Run time
build on ${{ matrix.os }} (${{ matrix.target }} - ${{ matrix.interpreter \|\| 'all' }}${{ (((matrix.os == 'linux') && format(' - {0}', (((matrix.manylinux == 'auto') && 'manylinux') \|\| matrix.manylinux))) \|\| '') }})	0s
rust benchmarks	3m 0s
build pgo-optimized on ${{ matrix.os }} / ${{ matrix.interpreter }}	0s
build sdist	13s
build-wasm-emscripten	2m 51s
coverage	3m 4s
lint	54s
test-debug 3.11	1m 2s
test on ubuntu	2m 2s
test-debug pypy3.10	1m 54s
test on macos	4m 23s
test-pydantic-integration	2m 14s
test on windows	4m 21s
test 3.7	2m 17s
test 3.8	2m 0s
test 3.9	2m 20s
test 3.10	2m 3s
test 3.11	2m 1s
test 3.12	2m 30s
test pypy3.7	2m 40s
test pypy3.8	2m 42s
test pypy3.9	2m 52s
test pypy3.10	2m 59s
test build on ${{ matrix.target }}-${{ matrix.distro }}	0s
test build on ${{ matrix.os }}	0s
inspect-pypi-assets	0s
check	2s
release	0s
	50m 24s

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