Replace MetadataDecodable macro

[reddevilmidzy]

MetadataDecodable was modified to BlobDecodable and LazyDecodable since: rust-lang/rust#149455

so CI failed

https://rustc-dev-guide.rust-lang.org/serialization.html#derive-macros

@rustbot label I-outdated

[tshepang]

are you happy to submit an update

[reddevilmidzy]

sure, I'm