feat: add comprehensive HTTP e2e tests covering connector, TLS, probeResist, idleTimeout, and UDP relay

Adds 12 new HTTP handler test scenarios: HTTP connector (no-auth, auth, TLS
upstream), CONNECT tunnel (no-sniffing, bypass-403), probeResist (host, web,
file, knock), idleTimeout, and UDP relay over HTTP. Introduces
RunGostContainerWithFiles helper for mounting extra files into test containers.

tests/e2e/testdata/http/server_metadata.yaml

@@ -0,0 +1,20 @@
+services:
+- name: http-proxy-meta
+  addr: :8080
+  handler:
+    type: http
+    auther: auther-0
+    metadata:
+      # probeResist: decoy response on auth failure (code:404 hides the proxy)
+      probeResist: code:404
+      # keepalive: enable HTTP keep-alive on upstream transport (parse test)
+      keepalive: true
+      # compression: enable HTTP compression on upstream transport (parse test)
+      compression: true
+  listener:
+    type: tcp
+authers:
+- name: auther-0
+  auths:
+  - username: user
+    password: pass