test: 补充单元测试覆盖率 29.9% → 36.6%

新建 18 个测试文件，追加 30 个已有测试文件，覆盖协议解析、
错误分类、CEL 表达式求值、YAML 反序列化、字节编码等纯函数。

plugins/services/oracle_test.go

@@ -0,0 +1,29 @@
+//go:build plugin_oracle || !plugin_selective
+
+package services
+
+import (
+	"errors"
+	"testing"
+)
+
+func TestClassifyOracleErrorType(t *testing.T) {
+	tests := []struct {
+		name string
+		err  error
+		want ErrorType
+	}{
+		{"nil error", nil, ErrorTypeUnknown},
+		{"ORA-01017 invalid username/password", errors.New("ORA-01017: invalid username/password"), ErrorTypeAuth},
+		{"TNS-12541 no listener", errors.New("TNS-12541 no listener"), ErrorTypeNetwork},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := classifyOracleErrorType(tt.err)
+			if got != tt.want {
+				t.Errorf("classifyOracleErrorType(%v) = %v, want %v", tt.err, got, tt.want)
+			}
+		})
+	}
+}