fix(backend): memory leak in memory caches (#14363)

* encapsulate `MemoryKVCache<T>`

* remove infinity caches

* encapsulate other caches

* add missing awaits to internally synchronize caches

* implement pull-through caching

* tune cache lifetimes

* optimize cache GC by stopping early

* summarize changes in CHANGELOG.md

* Fix timeout comments

Co-authored-by: かっこかり <67428053+kakkokari-gtyih@users.noreply.github.com>

* add comments about awaiting the redis write

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Co-authored-by: かっこかり <67428053+kakkokari-gtyih@users.noreply.github.com>

packages/backend/src/queue/processors/DeliverProcessorService.ts

@@ -45,7 +45,7 @@ export class DeliverProcessorService {
 		private queueLoggerService: QueueLoggerService,
 	) {
 		this.logger = this.queueLoggerService.logger.createSubLogger('deliver');
-		this.suspendedHostsCache = new MemorySingleCache<MiInstance[]>(1000 * 60 * 60);
+		this.suspendedHostsCache = new MemorySingleCache<MiInstance[]>(1000 * 60 * 60); // 1h
 	}
 
 	@bindThis