CustomMetadataV16 typedef
CustomMetadataV16 = CustomMetadataV15
V16 uses the same CustomMetadata structure as V15
Custom metadata fields remain unchanged between V15 and V16.
Reference: https://github.com/paritytech/frame-metadata/blob/main/frame-metadata/src/v16.rs#L47-L66
Implementation
typedef CustomMetadataV16 = CustomMetadataV15;