Speed up the vaultik and database package tests (closes #235)

In the Dockerfile test phase, internal/vaultik spent 23.6s of 31.9s in
36 tests run one at a time. 24 of them were serial only because they
call log.Initialize; they now call it before t.Parallel(), so the
logger is replaced before any parallel test runs. The 12 still serial
change the umask, TMPDIR, os.Stderr or time.Local.

TestLargeDatasets took 8.4s of the 9.8s internal/database run by
committing each of its 1,500 inserts on its own; it now makes them in
one transaction. TestDedupOnlySnapshotRestores gives its second backup
its own snapshot name instead of sleeping 1.1s for a new snapshot ID.

Model: opus-5-5

internal/database/repository_edge_cases_test.go

@@ -3,6 +3,7 @@ package database
 
 import (
 	"context"
+	"database/sql"
 	"fmt"
 	"strings"
 	"testing"
@@ -367,7 +368,7 @@ func verifyBlobNullUploadTS(
 }
 
 // createLargeDatasetFiles creates fileCount files and adds every other
-// one to the snapshot.
+// one to the snapshot, in one transaction as a backup writes them.
 func createLargeDatasetFiles(
 	t *testing.T,
 	repos *Repositories,
@@ -376,31 +377,38 @@ func createLargeDatasetFiles(
 ) {
 	t.Helper()
 
-	ctx := context.Background()
 	start := time.Now()
 
-	for i := range fileCount {
-		file := &File{
-			Path:  types.FilePath(fmt.Sprintf("/large/file%05d.txt", i)),
-			MTime: time.Now(),
-			Size:  int64(i * 1024),
-			Mode:  0644,
-			UID:   uint32(1000 + (i % 10)),
-			GID:   uint32(1000 + (i % 10)),
-		}
+	err := repos.WithTx(context.Background(),
+		func(ctx context.Context, tx *sql.Tx) error {
+			for i := range fileCount {
+				file := &File{
+					Path:  types.FilePath(fmt.Sprintf("/large/file%05d.txt", i)),
+					MTime: time.Now(),
+					Size:  int64(i * 1024),
+					Mode:  0644,
+					UID:   uint32(1000 + (i % 10)),
+					GID:   uint32(1000 + (i % 10)),
+				}
 
-		err := repos.Files.Create(ctx, nil, file)
-		if err != nil {
-			t.Fatalf("failed to create file %d: %v", i, err)
-		}
+				err := repos.Files.Create(ctx, tx, file)
+				if err != nil {
+					return fmt.Errorf("creating file %d: %w", i, err)
+				}
 
-		// Add half to snapshot
-		if i%2 == 0 {
-			err = repos.Snapshots.AddFileByID(ctx, nil, snapshotID, file.ID)
-			if err != nil {
-				t.Fatal(err)
+				// Add half to snapshot
+				if i%2 == 0 {
+					err = repos.Snapshots.AddFileByID(ctx, tx, snapshotID, file.ID)
+					if err != nil {
+						return err
+					}
+				}
 			}
-		}
+
+			return nil
+		})
+	if err != nil {
+		t.Fatal(err)
 	}
 
 	t.Logf("Created %d files in %v", fileCount, time.Since(start))