fix: restore chunk_bench_test.go (compiles without PrecomputeAttrs)

The benchmark never imported the telemetry package or used
PrecomputeAttrs/RecordRaw. It exercises NewFullFetchChunker, Slice,
and Close which are all unchanged.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: 2 people

packages/orchestrator/pkg/sandbox/block/chunk_bench_test.go

@@ -0,0 +1,60 @@
+package block
+
+import (
+	"context"
+	"path/filepath"
+	"testing"
+
+	sdkmetric "go.opentelemetry.io/otel/sdk/metric"
+
+	blockmetrics "github.com/e2b-dev/infra/packages/orchestrator/pkg/sandbox/block/metrics"
+)
+
+const (
+	cbBlockSize  int64 = 4096
+	cbNumBlocks  int64 = 16384 // 64 MiB
+	cbCacheSize  int64 = cbNumBlocks * cbBlockSize
+	cbChunkSize  int64 = 4 * 1024 * 1024 // 4 MiB — MemoryChunkSize
+	cbChunkCount int64 = cbCacheSize / cbChunkSize
+)
+
+// BenchmarkChunkerSlice_CacheHit benchmarks the full FullFetchChunker.Slice
+// hot path on a cache hit: bitmap check + mmap slice return + OTEL
+// timer.Success with attribute construction.
+func BenchmarkChunkerSlice_CacheHit(b *testing.B) {
+	provider := sdkmetric.NewMeterProvider()
+	b.Cleanup(func() { provider.Shutdown(context.Background()) })
+
+	m, err := blockmetrics.NewMetrics(provider)
+	if err != nil {
+		b.Fatal(err)
+	}
+
+	chunker, err := NewFullFetchChunker(
+		cbCacheSize, cbBlockSize,
+		nil, // base is never called on cache hit
+		filepath.Join(b.TempDir(), "cache"),
+		m,
+	)
+	if err != nil {
+		b.Fatal(err)
+	}
+	b.Cleanup(func() { chunker.Close() })
+
+	// Pre-populate the cache so every Slice hits.
+	chunker.cache.setIsCached(0, cbCacheSize)
+
+	ctx := context.Background()
+
+	b.ResetTimer()
+	for i := range b.N {
+		off := int64(i%int(cbChunkCount)) * cbChunkSize
+		s, sliceErr := chunker.Slice(ctx, off, cbChunkSize)
+		if sliceErr != nil {
+			b.Fatal(sliceErr)
+		}
+		if len(s) == 0 {
+			b.Fatal("empty slice")
+		}
+	}
+}