Cardano Updates

Transaction, TransactionBody, TransactionOutput and
TransactionWitnessSet fromCbor now accept { strict?: boolean }. When
strict, deserialization throws on unknown map keys so that
signing/summary paths can detect constructs from a newer era instead of
silently under-rendering them.

By default unknown keys are now properly skipped; previously their
values were left unconsumed, corrupting parsing of subsequent fields.

Closes #1684

Unknown CBOR discriminant values were misinterpreted instead of
rejected: an unknown drep kind deserialized as AlwaysNoConfidence,
unknown credential types and votes were accepted as-is, and an unknown
datum_option kind produced an empty datum. Constructs from a newer era
could therefore silently render as something else entirely.

Part of #1684