Add OcspChainValidationEvent DTO, OcspStatus enum, and OcspEventBuilder
helper with BuildPeerReject, BuildChainValidation, and ParseStatus methods.
Register OcspChainValidationEvent in EventJsonContext source-gen context.
Add OcspPeerReject and OcspChainValidation subject constants to EventSubjects.
10 new tests in OcspEventTests cover all DTOs, builder methods, status
parsing, and JSON round-trip.
