feat: Add HTTP/HTTPS/SOCKS proxy support

[maycon]

Summary

Add support for routing TRECO requests through HTTP, HTTPS, and SOCKS proxies. This is essential for:

• Intercepting traffic with Burp Suite / OWASP ZAP
• Testing through corporate proxies
• Anonymizing attack traffic
• Bypassing IP-based rate limiting

Proposed Configuration

config:
  proxy:
    url: "http://127.0.0.1:8080"
    # or
    http: "http://127.0.0.1:8080"
    https: "http://127.0.0.1:8080"
    socks: "socks5://127.0.0.1:1080"
    
    # Optional authentication
    username: "user"
    password: "pass"
    
    # Optional: bypass proxy for certain hosts
    no_proxy: ["localhost", "127.0.0.1", "*.internal.com"]

Use Cases

1. Security Testing: Route through Burp/ZAP to inspect requests
2. Corporate Environments: Required proxy for external access
3. Rate Limit Bypass: Rotate through multiple proxies
4. Anonymity: Hide source IP during authorized testing

Acceptance Criteria

• Support HTTP proxy
• Support HTTPS proxy
• Support SOCKS5 proxy
• Support proxy authentication
• Support no_proxy exclusion list
• Environment variable fallback (HTTP_PROXY, HTTPS_PROXY)
• CLI override (--proxy)
• Works with all connection strategies (preconnect, multiplexed, lazy, pooled)

Sub-issues

• feat(proxy): implement single proxy configuration #28
• feat(proxy): implement multi-proxy rotation #29

Technical Notes

httpx supports proxies natively:

client = httpx.Client(
    proxies={
        "http://": "http://127.0.0.1:8080",
        "https://": "http://127.0.0.1:8080",
    }
)

References

• httpx proxy docs: https://www.python-httpx.org/advanced/#http-proxying
• Burp Suite: https://portswigger.net/burp