chore: bump x to v0.15.1, add e2e tests for chainGroup and sniffing

- Bump github.com/go-gost/x v0.15.0 → v0.15.1
- ChainGroupSuite: matcher routing by host, probe dead-chain pre-marking
- SniffingSuite: SOCKS5+HTTPS w/o SNI, debug-only log on empty SNI
- Add RunHTTPSEchoContainer and https_echo.py test helper

tests/e2e/testdata/sniffing/no_sni.yaml

@@ -0,0 +1,9 @@
+services:
+  - name: service-0
+    addr: ":8080"
+    handler:
+      type: socks5
+      metadata:
+        sniffing: true
+    listener:
+      type: tcp