Mints a token for a Sisu person, bound to no account: the click while logged in creates the
binding. Returns the row id and the plaintext token for the mailed link.
Batch form of insert: mints one token per row in a single INSERT, at the caller-chosen
ids, in order. Each row still gets its own random plaintext token.
Seeds a token with a fixed plaintext value and a chosen expiry/claim state, which insert
cannot do: system tests need the valid, expired and used links to be constants. Seed use only.