refactor(flowcontrol): single-ended SafeQueue backed by container/heap #6104

Job	Run time
check-changes	6s
e2e-image-router (renderer)	1m 57s
e2e-image-common (builder)	54s
e2e-image-common (simulator)	11s
e2e-image-router (sidecar)	1m 54s
test	8m 33s
e2e-image-common (epp)	3m 28s
verify-helm-charts	0s
e2e-router (pd)	5m 26s
e2e-gaie (metrics)	6m 58s
e2e-router (pd-shared-storage-disagg)	5m 15s
e2e-router (extended)	14m 36s
e2e-router (pd-metrics)	4m 32s
e2e-gaie (traffic)	10m 27s
e2e-router (pd-shared-storage-deprecated)	5m 36s
e2e-router (disruption)	5m 20s
	1h 15m 13s

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