feat: route plugin HTTP traffic through SOCKS5 proxy

Add PySocks dependency and shared src/derp/http.py module providing
proxy-aware urlopen() and build_opener() that route through
socks5h://127.0.0.1:1080. Subclassed SocksiPyHandler passes SSL
context through to HTTPS connections.

Swapped 14 external-facing plugins to use the proxied helpers.
Local-only traffic (SearXNG, raw DNS/TLS sockets) stays direct.
Updated test mocks in test_twitch and test_alert accordingly.

plugins/wayback.py

@@ -7,6 +7,7 @@ import json
 import logging
 import urllib.request
 
+from derp.http import urlopen as _urlopen
 from derp.plugin import command
 
 log = logging.getLogger(__name__)
@@ -28,7 +29,7 @@ def _lookup(url: str, timestamp: str = "") -> dict:
     )
 
     try:
-        resp = urllib.request.urlopen(req, timeout=_TIMEOUT)
+        resp = _urlopen(req, timeout=_TIMEOUT)
         data = json.loads(resp.read().decode("utf-8"))
         resp.close()
         return data