fix(acme-http-client): Destroy keep-alive HTTP agents and DNS client on shutdown to allow process exit; add destroy() on AcmeHttpClient and AcmeClient, wire agents into requests, and call client/smartdns destroy during SmartAcme.stop; documentation clarifications and expanded README (error handling, examples, default retry values).

ts/acme/acme.classes.http-client.ts

@@ -17,11 +17,23 @@ export class AcmeHttpClient {
   private nonce: string | null = null;
   public kid: string | null = null;
   private logger?: TAcmeLogger;
+  private httpsAgent: https.Agent;
+  private httpAgent: http.Agent;
 
   constructor(directoryUrl: string, accountKeyPem: string, logger?: TAcmeLogger) {
     this.directoryUrl = directoryUrl;
     this.accountKeyPem = accountKeyPem;
     this.logger = logger;
+    this.httpsAgent = new https.Agent({ keepAlive: false });
+    this.httpAgent = new http.Agent({ keepAlive: false });
+  }
+
+  /**
+   * Destroy HTTP agents to release sockets and allow process exit.
+   */
+  destroy(): void {
+    this.httpsAgent.destroy();
+    this.httpAgent.destroy();
   }
 
   private log(level: string, message: string, data?: any): void {
@@ -186,6 +198,7 @@ export class AcmeHttpClient {
         path: urlObj.pathname + urlObj.search,
         method,
         headers: requestHeaders,
+        agent: isHttps ? this.httpsAgent : this.httpAgent,
       };
 
       const req = lib.request(options, (res) => {