fix(stores): MemoryStore/FileStore.exists() ignores expiry #7422

Job	Run time
Test server integration (uvicorn<0.27.0)	44s
pyright	33s
test_typing_extensions (4.13.1)	21s
Test Minimal Application with Base Dependencies	20s
slotscheck	21s
validate	13s
test_typing_extensions (latest)	21s
test (3.13) / test	2m 13s
test_typing_extensions (4.12.1)	18s
mypy	41s
test (3.11) / test	2m 30s
test (3.14) / test	1m 59s
test (3.12) / test	2m 55s
test_typing_extensions (4.14.0)	21s
Test server integration (uvicorn>=0.27.0)	46s
test-platform-compat	0s
build-docs	3m 3s
test_success	2s
upload-test-coverage	17s
	17m 58s

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