fix(rpc): Return detailed errors to the RPC client when a block proposal fails

[teor2345]

Motivation

We are currently testing Zebra's block templates in ticket #5803. But I can't work out if Zebra's errors are expected or the same as zcashd, because it doesn't return any error information at all.

This PR changes the error handling from bug #5981, it probably gets us closer to a fix.
(But to match zcashd we'd need to stop pretty printing, and change the format of the error string.)

Specifications

We can do whatever we like here, because bug #5981 will fix up any mining pool compatibility issues.

Solution

• Send the RPC client the kind of error, and the detailed error debug information

Review

This seems like a high priority because testing is difficult without it.

Reviewer Checklist

• Will the PR name make sense to users?
  • Does it need extra CHANGELOG info? (new features, breaking changes, large changes)
• Are the PR labels correct?
• Does the code do what the ticket and PR says?
  • Does it change concurrent code, unsafe code, or consensus rules?
• How do you know it works? Does it have tests?

[teor2345]

I tested this PR with zcash-rpc-block-template-to-proposal.

I now see detailed errors like:

invalid proposal: Block {
    source: ValidateProposal(
        "proposal is not based on the current best chain tip: previous block hash must be the best chain tip",
    ),
}

Rather than the same error every time:

{
  "reject_reason": "rejected",
  "capabilities": [
    "proposal"
  ]
}

[codecov]

Codecov Report

Merging #5993 (fde6d52) into main (256b1c0) will increase coverage by 0.04%.
The diff coverage is 0.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5993      +/-   ##
==========================================
+ Coverage   77.94%   77.98%   +0.04%     
==========================================
  Files         312      312              
  Lines       38987    38995       +8     
==========================================
+ Hits        30387    30410      +23     
+ Misses       8600     8585      -15     

[arya2]

This looks great!

Only change needed is an updated reference in the acceptance test for the renamed ErrorResponse.