RpcMetadataCompanion

User-facing metadata entry point, mirroring commons RpcMetadataCompanion. A concrete metadata class's COMPANION mixes this in, parameterized by the metadata type constructor M[_], to expose materialize[Real]: M[Real] — the metadata-class-param-driven derivation.

Example (research §"Code Examples"):

 final case class TraitMeta[T](
   @reifyName name: String,
   @rpcMethodMetadata @multi methods: List[MethodMeta[?]],
 )
 object TraitMeta extends RpcMetadataCompanion[TraitMeta]
 // ...
 val md: TraitMeta[SampleApi] = TraitMeta.materialize[SampleApi]

The macro reads M's primary-constructor params, classifies each by its steering annotation, and fills it from the real trait's halotukozak.made.Done structure — reusing RpcName.computeAll for resolved names so metadata names cannot drift from the engine's.