Provide standard middlewares for Blockchain primitive types

[MHHukiewitz]

When parsing non-javascript primitives, such as larger-than-52-bytes integers, we resort to types such as BN from bn.js (or sometimes bignumber.js in Ethereum's SDK).

Besides parsing from buffer-layout, IDL, or ABI, we need to

• unify between very similar types (like BN and BigNumber)
• define a common middleware that handles SerDe for these types between microservices

https://borsh.io/ (then 'Specification') gives a good overview of what types we are talking about in Solana (and also Near and similar chains).

The most important culprit here is still BN, so I would also consider this issue to be mostly done when BNs are being correctly serialized and then deserialized as a BN into the indexer.