fix(mail): add periodic cleanup timers and proper shutdown handling for bounce manager and delivery queue; avoid mutating maps during iteration and prune stale rate-limiter stats to prevent memory growth

ts/00_commitinfo_data.ts

@@ -3,6 +3,6 @@
  */
 export const commitinfo = {
   name: '@push.rocks/smartmta',
-  version: '5.3.0',
+  version: '5.3.1',
   description: 'A high-performance, enterprise-grade Mail Transfer Agent (MTA) built from scratch in TypeScript with Rust acceleration.'
 }