backend: return error message from Etherscan.

[bznein]

If we return the unmarshaling error, the fronted might show the user an error that is confusing and not helpful. By returning the actual error, there is a change the user might figure out what's wrong on their own. And even if they don't, it would be easier for support to troubleshoot.

Before asking for reviews, here is a check list of the most common things you might need to consider:

• updating the Changelog
• writing unit tests
• checking if your changes affect other coins or tokens in unintended ways
• testing on multiple environments (Qt, Android, ...)
• having an AI review your changes

[thisconnect]

Tested very nice, I patched an older version 4.47.2 as you suggested
(Note: can't use a nova for testing 😅 )

this error is looks very useful (compared to unmarshal)

[Beerosagos]

utACK