Don't parse, verify #605
Description
All extrinsics which use the BTC-Relay require "raw" (Vec<u8>) values which are parsed at runtime. In the past this has led to a range of unhandled panics we have caught during fuzzing. Once decoded these types are then re-encoded for verification which is an unnecessary overhead. We should instead use the concrete types which should also allow us to better determine the weights of the extrinsics.