savesAndLoadsTerm_atPlausibilityEdges

Mirrors RaftEngine.checkedRestoredTerm (#1855): the engine admits a restored storage.term() in 0..MAX_PLAUSIBLE and refuses to start outside it.

A term is a Long and both endpoints are admitted, so an adapter whose term column cannot hold one — a 32-bit integer, a REAL/Double, a JSON number in a JS-backed store — silently hands the engine a different node identity than the one it persisted, which is a double-vote in a term the node has forgotten (§5.2).