change(utils): Add a direct connection mode to zebra-checkpoints

[teor2345]

Instructions

Test the new direct JSON-RPC connections using:

cargo run --release --features=zebra-checkpoints --bin zebra-checkpoints -- --transport direct --addr 127.0.0.1:<zebrad port>

And the refactored existing functionality using:

cargo run --release --features=zebra-checkpoints --bin zebra-checkpoints -- --transport cli --addr 127.0.0.1:<zebrad port>
# automatically uses zcashd
cargo run --release --features=zebra-checkpoints --bin zebra-checkpoints -- --transport cli --backend zcashd
# actually uses zcashd, but in zebrad RPC parameter mode
cargo run --release --features=zebra-checkpoints --bin zebra-checkpoints -- --transport cli --backend zebrad

Motivation

In #6367 we want to generate checkpoints in CI. This is the Rust tool part of that ticket.

Complex Code or Requirements

There are 4 modes in this tool now:

• zebrad direct
• zcashd CLI
• zebrad CLI
• zcashd CLI in zebrad mode (not supported but it should work)

This means we need to test all of them. (Which I've done.)

Technically this code is async, but it doesn't actually use much concurrency.

Solution

• Move all the CLI-specific code into a single function
• Add transport and addr arguments to zebra-checkpoints
• Make zebra-checkpoints support both CLI and direct JSON-RPC connections
• Document required features

Related Changes:

• simplify the zebra-checkpoints implementation
• Add a json-conversion feature for converting JSON to valid Heights
  • Add a TryIntoHeight convenience trait for converting integers, strings, and JSON to valid heights (we'll use this in other fixes like [NCC-E005955-XVE] zebra-chain: Inconsistent error management in Add and Sub for Height #6279)
• Move the RpcRequestClient into zebra-node-services, behind a new feature

Unrelated cleanups:

• Replace a custom function with an existing dependency function

Testing

• Add a checkpoint list test for minimum height gaps

The rest of the testing will happen as part of the next PR which puts this in CI.

Review

This is part of a routine release process simplification change.

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?

Follow Up Work

Add this new tool to CI, so we always have checkpoints ready for releases.
Fully test the generated checkpoints.

[codecov]

Codecov Report

Merging #6516 (838a98d) into main (7681da3) will increase coverage by 0.30%.
The diff coverage is 37.73%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6516      +/-   ##
==========================================
+ Coverage   77.72%   78.03%   +0.30%     
==========================================
  Files         307      307              
  Lines       40282    40256      -26     
==========================================
+ Hits        31310    31414     +104     
+ Misses       8972     8842     -130     

[upbqdn]

Looks great. I left a couple of minor suggestions and questions.