Add sfdupes info: show the database's details (closes #117)

info prints the database's path and source, the sizes of the database
file and its -wal file, when the database file last changed, the schema
version and the record counts, one per line as a name, a tab and the
value. It opens the database as report does and shows an open and a
count phase on stderr. The schema version and the counts come from one
read-only transaction, the counts from one query.

seedDatabase now closes test databases out of WAL mode, as scan does;
otherwise info's own connection creates an empty -wal file. The open
phase's name and text became constants for the linter, and the scan
command moved to newScanCommand to keep newRootCommand short enough.

Judgement call: the lines are written after the last display ends, so they skip the display's stdout writer.

Model: opus-5-5

trees.go

@@ -28,7 +28,7 @@ type treeNode struct {
 // as "[2/4] read", for the phase's progress display. The list here is
 // the one place the phases are counted.
 func treesPhase(name string) string {
-	return phaseLabel([]string{"open", "read", "group", "write"}, name)
+	return phaseLabel([]string{openPhase, "read", "group", "write"}, name)
 }
 
 // runTrees implements the trees subcommand: it reads every record from
@@ -57,8 +57,8 @@ func runTrees(ctx context.Context, stdout io.Writer) error {
 	// Opening can wait on a busy database for as long as the busy
 	// timeout.
 	prog := newProgress(progressParams{
-		label: treesPhase("open"), total: -1,
-		waitingFor: "opening the database",
+		label: treesPhase(openPhase), total: -1,
+		waitingFor: openingDatabase,
 	})
 	db, err := openReportDatabase(ctx, dbPath)