rpc: replace default encoding from Binary to Base64

[fanatid]

Problem

Right now JS library use base64 as the default encoding and solana-client do not use Binary/Base64 as the default encoding. But RPC still assumes Binary as default which has a length limitation of encoding account data (128 bytes).

Summary of Changes

This PR change UiAccountEncoding::Binary is few RPC methods to UiAccountEncoding::Base64.

[CriesofCarrots]

I totally agree with the impetus here, but unfortunately these are technically breaking changes for cases where users do not supply an encoding parameter, and violate our backward compatibility policy. (With the exception of the test change. That one we could totally do, but there's no great reason to.)
Sorry. That said, we are discussing establishing a JSON-RPC spec, and this is absolutely something we can fix in that "v2" implementation.

[fanatid]

Yeah, it would be a breaking change. Any ETA for v2? 😬

[CriesofCarrots]

Yeah, it would be a breaking change. Any ETA for v2? 😬

No specific timeline yet, but definitely follow that issue I linked: solana-foundation/specs#22
Okay if I close this?

[fanatid]

Yeah, let's close it 🙂