This is the fix that's specific to blockSchema.transactions, and needs to be refactored to be more general.
It's checking if the first value in the transactions array is a hash or a transaction object and uses the corresponding schema

Originally posted by @spacesailor24 in #5363 (comment)

Additionally, if one of the schemas defined by oneOf is an array of items that need to be formatted (e.g. blockSchema.transacitons), they're not currently being formatted i.e. When formatting a block the array of transaction hashes or object will always be returned using hex strings instead of whatever data format the user specifies

#5363 (review)