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/chaingroup/matcher.yaml

@@ -0,0 +1,48 @@
+services:
+- name: proxy
+  addr: :8080
+  handler:
+    type: http
+    chainGroup:
+      chains:
+        - chain: chain-target
+          matcher:
+            rule: Host(`tcp-echo`)
+        - chain: chain-other
+          matcher:
+            rule: Host(`no-match`)
+      selector:
+        strategy: round
+        maxFails: 1
+        failTimeout: 10s
+  listener:
+    type: tcp
+
+# Live relay: forwards to echo server.
+- name: relay
+  addr: 127.0.0.1:18081
+  handler:
+    type: http
+  listener:
+    type: tcp
+
+chains:
+- name: chain-target
+  hops:
+  - name: hop-target
+    nodes:
+    - name: n-live
+      addr: 127.0.0.1:18081
+      connector:
+        type: http
+
+# This chain has a dead relay — but the matcher Host("no-match") ensures it is
+# never selected for requests targeting tcp-echo.
+- name: chain-other
+  hops:
+  - name: hop-other
+    nodes:
+    - name: n-dead
+      addr: 127.0.0.1:18082
+      connector:
+        type: http

tests/e2e/testdata/chaingroup/probe.yaml

@@ -0,0 +1,52 @@
+services:
+- name: proxy
+  addr: :8080
+  handler:
+    type: http
+    chainGroup:
+      chains:
+        - chain: chain-live
+          probe:
+            type: tcp
+            addr: 127.0.0.1:18081
+            interval: 3s
+        - chain: chain-dead
+          probe:
+            type: tcp
+            addr: 127.0.0.1:18082
+            interval: 3s
+      selector:
+        strategy: round
+        maxFails: 1
+        failTimeout: 10s
+  listener:
+    type: tcp
+
+# Live relay: forwards to echo server.
+- name: relay
+  addr: 127.0.0.1:18081
+  handler:
+    type: http
+  listener:
+    type: tcp
+
+chains:
+- name: chain-live
+  hops:
+  - name: hop-live
+    nodes:
+    - name: n-live
+      addr: 127.0.0.1:18081
+      connector:
+        type: http
+
+# Dead chain: relay never listens here. TCP probe marks the chain entry so
+# FailFilter excludes it before real traffic reaches it.
+- name: chain-dead
+  hops:
+  - name: hop-dead
+    nodes:
+    - name: n-dead
+      addr: 127.0.0.1:18082
+      connector:
+        type: http