HotStuffGossipDiagnosticsJsonCodecs

Projection-local JSON codecs for diagnostics snapshots.

Import these givens only at projected-diagnostics encode/decode call sites. The local BigNat and String codecs intentionally differ from the core codecs, and the local Vector decoder adds a diagnostics-specific entry cap. These can conflict if imported into a scope that also summons the default core JSON codecs. The value-type codecs for ChainId, GossipTopic, and ValidatorSetHash are likewise intended only for this projected diagnostics surface.