fix: resolve benchmark and build tag conflicts

- Remove duplicate hash_selector.go (build tags handle switching)
- Fix benchmark to use worker.DirOverallSHA256Hex
- Fix snapshot_store.go to use integrity.DirOverallSHA256Hex directly
- Native tests pass, benchmarks now correctly test native vs Go

internal/worker/hash_selector.go

@@ -1,19 +0,0 @@
-package worker
-
-import (
-	"github.com/jfraeys/fetch_ml/internal/worker/integrity"
-)
-
-// dirOverallSHA256Hex uses native implementation when compiled with -tags native_libs.
-// The build tag selects between native_bridge.go (stub) and native_bridge_libs.go (real).
-// No runtime configuration needed - build determines behavior.
-func dirOverallSHA256Hex(root string) (string, error) {
-	// native_bridge_libs.go provides this when built with -tags native_libs
-	// native_bridge.go provides stub that falls back to Go
-	return dirOverallSHA256HexNative(root)
-}
-
-// DirOverallSHA256HexParallel exports the parallel directory hashing function.
-func DirOverallSHA256HexParallel(root string) (string, error) {
-	return integrity.DirOverallSHA256HexParallel(root)
-}

internal/worker/snapshot_store.go

@@ -173,7 +173,7 @@ func ResolveSnapshot(
 		return "", err
 	}
 
-	got, err := dirOverallSHA256Hex(extractDir)
+	got, err := integrity.DirOverallSHA256Hex(extractDir)
 	if err != nil {
 		return "", err
 	}

tests/benchmarks/dataset_size_comparison_test.go

@@ -48,7 +48,8 @@ func BenchmarkDatasetSizeComparison(b *testing.B) {
 			b.ResetTimer()
 			b.ReportAllocs()
 			for i := 0; i < b.N; i++ {
-				_, err := worker.DirOverallSHA256HexParallel(tmpDir)
+				// Use DirOverallSHA256Hex which calls native via build tag
+				_, err := worker.DirOverallSHA256Hex(tmpDir)
 				if err != nil {
 					b.Fatal(err)
 				}