feat(spooler): Implement eviction algorithm for `EnvelopeBuffer` #14950

Job	Run time
Lint Rust Default Features	1m 23s
Lint	3m 0s
Setup build metadata	1s
Test (macos-latest)	2m 3s
Test All Features (ubuntu-latest)	3m 0s
Test (windows-latest)	2m 45s
Integration Tests	3m 0s
Test Python	1m 27s
Build Relay Binary (relay, x86_64-unknown-linux-gnu)	2m 48s
Build Docker Image	1s
Publish Relay to DockerHub	1s
Publish Relay to GCR	1s
Upload build artifacts to gocd	1s
Sentry-Relay Integration Tests	1s
self-hosted-end-to-end	1s
	19m 33s

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