perf(heartbeat): schedule retry promotion from durable deadlines

Co-Authored-By: Paperclip <noreply@paperclip.ing>

server/src/modules/run-dispatch/application/use-cases.test.ts

@@ -12,6 +12,7 @@ function fakeReader(dueRuns: DueRetryRun[] = []): ScheduledRetryReader & { evalu
   const evaluateCalls: unknown[] = [];
   return {
     evaluateCalls,
+    async nextScheduledRetryAt() { return null; },
     async evaluateScheduledRetryGate(input) {
       evaluateCalls.push(input);
       return { allowed: true };