Return data from Solana Anchor program is now a List, rather than a String

[raymond0]

espresso-cash-public/packages/solana/lib/src/rpc/dto/return_data.dart

Line 20 in b920d79

final String data;

If an anchor program returns data, it now comes back as a list with the base64 encoding, and a 'base64' string, rather than just a String on its own. As a result, this decode throws an exception.

It's also possible to return a wide range of types, so I'm not sure of the best approach here.

Locally I've converted this to a dynamic type, however I'm not sure of the precise fix you'd want here. LMK and I'll submit a PR.