test: 新增主路径集成基准（EmitSync，真实 RSQL）

FilterProject/MultiFieldFilter/ComputedFields/StringConcat/NoFilter，
用 EmitSync 同步测端到端每行延迟（用户实际调用路径）。

streamsql_perf_test.go

@@ -0,0 +1,69 @@
+package streamsql
+
+import (
+	"testing"
+)
+
+// Integration benchmarks exercising the full main path with realistic RSQL.
+// EmitSync processes each row synchronously end-to-end (the same path users
+// call), so ns/op is the true per-row latency through ProcessData -> field
+// evaluation -> result building. Aggregation queries are exercised separately
+// via the Emit-based benchmarks.
+
+func benchEmitSync(b *testing.B, sql string, row map[string]interface{}) {
+	b.Helper()
+	ssql := New()
+	defer ssql.Stop()
+	if err := ssql.Execute(sql); err != nil {
+		b.Fatalf("Execute: %v", err)
+	}
+
+	// Warm up compile/preprocess caches (do not measure).
+	if _, err := ssql.EmitSync(row); err != nil {
+		b.Fatalf("warmup EmitSync: %v", err)
+	}
+
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		if _, err := ssql.EmitSync(row); err != nil {
+			b.Fatalf("EmitSync: %v", err)
+		}
+	}
+	b.StopTimer()
+}
+
+func BenchmarkMainPath_FilterProject(b *testing.B) {
+	benchEmitSync(b,
+		"SELECT deviceId, temperature FROM stream WHERE temperature > 20",
+		map[string]interface{}{"deviceId": "d1", "temperature": 25.5, "humidity": 60.0},
+	)
+}
+
+func BenchmarkMainPath_MultiFieldFilter(b *testing.B) {
+	benchEmitSync(b,
+		"SELECT deviceId, temperature, humidity FROM stream WHERE temperature > 20 AND humidity < 80",
+		map[string]interface{}{"deviceId": "d1", "temperature": 25.5, "humidity": 60.0},
+	)
+}
+
+func BenchmarkMainPath_ComputedFields(b *testing.B) {
+	benchEmitSync(b,
+		"SELECT deviceId, temperature * 2 + humidity AS score, abs(temperature - 100) AS dev FROM stream WHERE temperature > 20",
+		map[string]interface{}{"deviceId": "d1", "temperature": 25.5, "humidity": 60.0},
+	)
+}
+
+func BenchmarkMainPath_StringConcat(b *testing.B) {
+	benchEmitSync(b,
+		"SELECT deviceId + '-' + location AS id FROM stream",
+		map[string]interface{}{"deviceId": "d1", "location": "roomA"},
+	)
+}
+
+func BenchmarkMainPath_NoFilter(b *testing.B) {
+	benchEmitSync(b,
+		"SELECT deviceId, temperature, humidity FROM stream",
+		map[string]interface{}{"deviceId": "d1", "temperature": 25.5, "humidity": 60.0},
+	)
+}