feat(spool): Check preconditions before unspooling #15321

Job	Run time
Lint Rust Default Features	1m 29s
Lint	3m 1s
Test (macos-latest)	2m 18s
Test All Features (ubuntu-latest)	3m 39s
Setup build metadata	1s
Test (windows-latest)	6m 46s
Integration Tests	12m 12s
Test Python	1m 11s
Build Relay Binary (relay, x86_64-unknown-linux-gnu)	7m 59s
Build Docker Image (relay)	32s
Sentry-Relay Integration Tests	11m 51s
Publish Relay to DockerHub	0s
self-hosted-end-to-end	13m 43s
Publish Relay to GCR	0s
Upload build artifacts to gocd	0s
	1h 4m 42s

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