In building a raw transaction how is the base64 format of a signature incorporated into the transaction.
It's not, there's no base64 representation of signatures used in Bitcoin consensus or transactions.
Message signing using P2PKH with
signmessage in Bitcoin Core and other tools uses a feature of ECDSA which was re-discovered after the creation of the software called pubkey recovery, this is frequently but not always encoded as base64 as a human compatible representation. It is not used anywhere else.
one DER format
The original releases of Bitcoin effectively used ASN.1 BER, and this was reduced to a strict definition of DER in BIP66. In effect we don't use ASN.1 all, but a very restricted subset of it due to consensus issues surrounding using a lengthy, poorly defined, and malleable specification.
I really don't understand why there is a move to make a currency so complex when the original intention was for it to alleviate the economic pain and hardship on earth.
Your misunderstanding of Bitcoin is hubris, not unnecessary complexity.