Handle cross-thread slab frees #517

Job	Run time
security / license-gate	2m 45s
security / security-static	30s
lint / lint	4m 47s
security / codeql-gate	38m 18s
test / setup-matrix	4s
test / test-windows-guards	7m 26s
test / test-windows (windows-latest, CLANG64, x86_64)	27m 40s
test / test-unix (macos-14, cc, c++)	10m 31s
test / test-unix (macos-15-intel, cc, c++)	19m 18s
test / test-unix (ubuntu-24.04-arm, gcc, g++)	1h 10m 32s
test / test-unix (ubuntu-latest, gcc, g++, true)	16m 24s
ci-ok	2s
	3h 18m 17s

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