logEntryIndexAndTerm_roundTripAtPlausibilityCeiling

Mirrors the range half of RaftEngine.checkedRestoredEntries (#1887): a restored LogEntry.index is admitted in 0..MAX_PLAUSIBLE and a LogEntry.term in 0..currentTerm, itself bounded by the same ceiling.

Same precision reasoning as snapshotMeta_roundTripsAtPlausibilityCeiling — the run spans MAX_PLAUSIBLE - 2 .. MAX_PLAUSIBLE, so it covers the inclusive boundary and the two neighbours a Double cannot represent, while staying contiguous (which is separately required, below). The final read also exercises RaftStorage.entries with a fromIndex past Int.MAX_VALUE — the shape the engine's own entries(snapshotIndex + 1) takes on a compacted node, and one an adapter comparing through a 32-bit column gets wrong.