Don't enable HTTP keepalive by default

HTTP keepalive was enabled by default in Node 20, and is apparently causing errors for axios. See e.g. nodejs/node#47130, axios/axios#6113

lib/utils/http.js

@@ -1,6 +1,8 @@
 import assert from "assert";
 import axios from "axios";
 import config from "exp-config";
+import http from "http";
+import https from "https";
 import { debugMeta, logger } from "lu-logger";
 import util from "util";
 
@@ -9,6 +11,11 @@ import getUrl from "./get-url.js";
 
 const backends = buildBackends();
 
+const httpAgent = new http.Agent({ keepAlive: false });
+const httpsAgent = new https.Agent({ keepAlive: false });
+const httpAgentKeepAlive = new http.Agent({ keepAlive: true });
+const httpsAgentKeepAlive = new https.Agent({ keepAlive: true });
+
 async function performRequest(method, params) {
   assert(config.appName, "appName must be set in config");
 
@@ -46,6 +53,14 @@ async function performRequest(method, params) {
     opts.paramsSerializer = params.paramsSerializer;
   }
 
+  if (params.keepAlive) {
+    opts.httpAgent = httpAgentKeepAlive;
+    opts.httpsAgent = httpsAgentKeepAlive;
+  } else {
+    opts.httpAgent = httpAgent;
+    opts.httpsAgent = httpsAgent;
+  }
+
   let response;
   try {
     response = await axios(url, opts);