verificationKey as base64 and signature helpers to snarkyjs

[Trivo25]

• checkAccountUpdateSignature to verify the signature for an account update
• exports the verificationKey of a zkApp account in ~~base58~~ base64 format and its hash
• now uses base64 entirely

Companion of https://github.com/o1-labs/snarkyjs/pull/421

[Trivo25]

!ci-build-me

[psteckler]

We're using Base64 in the archive database for verification keys, which is faster than using Base58Check.

Encoding time of a key:

BASE58: 0.024964
BASE64: 0.000017

Encoding + decoding time:

BASE58: 0.048735
BASE64: 0.000078

Is it possible to use Base64 in SnarkyJS, so we have uniformity, and best performance?

The Base64 string is the base64 encoding of the Bin_prot-serialization of the key.

[Trivo25]

cc @mitschabaude how much of an issue would it be to use base64 instead? I am unsure of the scope

[bkase]

seems useful for us to have the base64 {en,de}coder support on the SnarkyJS side given that the protocol is moving towards using this in more places anyway so it's probably worth handling sooner rather than later