feat(metricstore): add running-stat fields to buffer

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

pkg/metricstore/stats_test.go

@@ -0,0 +1,30 @@
+// Copyright (C) NHR@FAU, University Erlangen-Nuremberg.
+// All rights reserved. This file is part of cc-backend.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package metricstore
+
+import (
+	"math"
+	"testing"
+)
+
+func TestNewBufferStatsInitialized(t *testing.T) {
+	b := newBuffer(100, 10)
+	if b.statSamples != 0 {
+		t.Errorf("statSamples = %d, want 0", b.statSamples)
+	}
+	if b.statSum != 0 {
+		t.Errorf("statSum = %v, want 0", b.statSum)
+	}
+	if b.statMin != math.MaxFloat32 {
+		t.Errorf("statMin = %v, want MaxFloat32 sentinel", b.statMin)
+	}
+	if b.statMax != -math.MaxFloat32 {
+		t.Errorf("statMax = %v, want -MaxFloat32 sentinel", b.statMax)
+	}
+	if !b.statsValid {
+		t.Error("statsValid = false, want true for a fresh empty buffer")
+	}
+}