feat: Add CONNECT tunneling support for HTTP proxy in sandboxed environments (#791)

This PR is a follow-up of PR #788, which unfortunately didn't fully fix
the use of **apify-cli** in Claude Code sandbox (in the browser, not the
local one).

Currently, this is what's happening :

1. Proxy receives the request
2. Proxy returns: HTTP/1.1 301 Moved Permanently
3. Location: https://api.apify.com:443/v2/users/me (adds explicit :443
port)
4. axios follows redirect to https://api.apify.com:443/v2/users/me
5. Proxy strips the :443 and redirects back to
https://api.apify.com/v2/users/me
6. **Infinite loop!**

This is a known `axios` problem, referenced in several **unsolved**
issues :
- axios/axios#6725
- axios/axios#2072
- axios/axios#925
- axios/axios#4531

To fix this issue, this PR adds support for CONNECT tunneling through
HTTP/HTTPS proxies, using
[proxy-agents](https://github.com/TooTallNate/proxy-agents) modules.

What this does :
1. HttpsProxyAgent sends CONNECT api.apify.com:443
2. Proxy establishes tunnel (returns 200 OK)
3. Client does TLS handshake through tunnel
4. Encrypted traffic flows through tunnel
5. Proxy cannot see/modify the HTTPS traffic (acts like classic proxy)
6. **No redirects, no loops!**

~By precaution, we keep here the current http[s] agent implementation
when the `HTTP[S]_PROXY` env vars are not defined.~ (Changed since
commit 89571f9)

Author: tducret

package-lock.json

@@ -71,6 +71,7 @@
         "axios": "^1.6.7",
         "content-type": "^1.0.5",
         "ow": "^0.28.2",
+        "proxy-agent": "^6.5.0",
         "tslib": "^2.5.0",
         "type-fest": "^4.0.0"
     },

package.json

@@ -1,11 +1,12 @@
-import http from 'node:http';
-import https from 'node:https';
+import type http from 'node:http';
+import type https from 'node:https';
 import os from 'node:os';
 
 import type { RetryFunction } from 'async-retry';
 import retry from 'async-retry';
 import type { AxiosError, AxiosInstance, AxiosRequestConfig, AxiosResponse, InternalAxiosRequestConfig } from 'axios';
 import axios, { AxiosHeaders } from 'axios';
+import { ProxyAgent } from 'proxy-agent';
 
 import { APIFY_ENV_VARS } from '@apify/consts';
 import type { Log } from '@apify/log';
@@ -74,8 +75,11 @@ export class HttpClient {
                 scheduling: 'lifo',
             };
 
-            this.httpAgent = new http.Agent(agentOptions);
-            this.httpsAgent = new https.Agent(agentOptions);
+            // Use ProxyAgent which automatically detects proxy from environment variables
+            // and supports CONNECT tunneling
+            const proxyAgent = new ProxyAgent(agentOptions);
+            this.httpAgent = proxyAgent;
+            this.httpsAgent = proxyAgent;
 
             // Disable Nagle's algorithm for lower latency
             // This sends data immediately instead of buffering small packets
@@ -90,6 +94,8 @@ export class HttpClient {
         this.axios = axios.create({
             httpAgent: this.httpAgent,
             httpsAgent: this.httpsAgent,
+            // Disable axios's built-in proxy handling since we're using custom agents
+            proxy: false,
             paramsSerializer: (params) => {
                 const formattedParams: [string, string][] = Object.entries<string | Date>(params)
                     .filter(([, value]) => value !== undefined)