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

progress.go

@@ -51,6 +51,14 @@ const barMargin = barWidth + 11
 // says while it counts them, before it has its total.
 const countingRecords = "counting the records"
 
+// openPhase is the name of the phase in which report, trees and info
+// open the database, and openingDatabase what its display says while
+// it does.
+const (
+	openPhase       = "open"
+	openingDatabase = "opening the database"
+)
+
 // stderrIsTTY reports whether stderr is attached to a terminal.
 func stderrIsTTY() bool {
 	return term.IsTerminal(int(os.Stderr.Fd()))