feat: 统一服务缓存 + 指纹驱动插件匹配

将 webServiceCache 扩展为通用 serviceCache，所有指纹识别结果
统一缓存，插件匹配时端口不命中则回退到服务名称匹配。

删除多余的 service_cache.go，复用已有的 ServiceInfo 体系。
补充 nil 防御、Explicit 标记、大量单元/集成/回归测试。

plugins/services/protocol_ids_test.go

@@ -0,0 +1,46 @@
+package services
+
+import (
+	"sync"
+	"testing"
+)
+
+func TestProtocolIDsAreConcurrentSafe(t *testing.T) {
+	const workers = 64
+	const perWorker = 64
+
+	tests := []struct {
+		name string
+		next func() uint32
+	}{
+		{"mongodb", nextRequestID},
+		{"kafka", func() uint32 { return uint32(nextKafkaCorrelationID()) }},
+		{"cassandra", func() uint32 { return uint32(nextCQLStreamID()) }},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var wg sync.WaitGroup
+			values := make(chan uint32, workers*perWorker)
+			for i := 0; i < workers; i++ {
+				wg.Add(1)
+				go func() {
+					defer wg.Done()
+					for j := 0; j < perWorker; j++ {
+						values <- tt.next()
+					}
+				}()
+			}
+			wg.Wait()
+			close(values)
+
+			seen := make(map[uint32]struct{}, workers*perWorker)
+			for value := range values {
+				if _, ok := seen[value]; ok {
+					t.Fatalf("duplicate protocol id %d", value)
+				}
+				seen[value] = struct{}{}
+			}
+		})
+	}
+}