1.14.0 — 99.5% of real proto3

Three more constructs now generate: message members inside a oneof (the common shape of a oneof — 19% of the googleapis corpus alone), optional on a message field (a no-op label in proto3), and enums sharing a value name (prefixed rather than refused).

Two of the three were refusals whose reasoning had expired: written before generated destructors existed, and never revisited.

Measured end to end for the first time: protogen parses and emits 99.5% of 7,301 real googleapis schemas. Earlier figures measured only parsing.