SQLite reuses one message for errors that need different responses: "database
is locked" is both SQLITE_BUSY, which busy_timeout retries, and
SQLITE_BUSY_SNAPSHOT, which it can never retry because the transaction's read
snapshot is already stale. Reading only the message, the two are
indistinguishable, and a lock error seen in the wild could not be diagnosed
without guessing which one it was.
Add db.ErrorCodes to unwrap a sqlite3.Error and report its result and extended
result codes, and include them in the SQL error log. The helper lives in db
because that package already owns the driver, so persistence does not need to
import it. Constraint, readonly and disk-full errors share messages the same
way, so this applies to every failed statement, not just locks.
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