PoX-4 signer key read/write with base Rust tests

[MarvinJanssen]

Description

This PR adds pox4 signer key read/write and useful helpers to interact with pox4 functions. The focus is to add base Rust tests to be used as a foundation for upcoming work items like #4059, #4058, #4147, and so on. There is also a basic check to make sure that a signer key is 33 bytes and to prevent key reuse.

Applicable issues

• [stacks-core] Update .pox-4 to properly handle stacker's signing key registration #3970
• Test Setup [common pox_4 catch-up] #4207

Additional info (benefits, drawbacks, caveats)

I kept this PR as narrow as possible for the purpose of unblocking other work and to (hopefully) make a merge straightforward. Processing the signer keys, calculating the aggregate key, and the signer StackerDB work is slated for subsequent PRs.

Comprehensive PoX4 smart contract tests will also be introduced in a different PR. (Pending clarunit tooling.)

Checklist

• Test coverage for new or modified code paths
• Changelog is updated
• Required documentation changes (e.g., docs/rpc/openapi.yaml and rpc-endpoints.md for v2 endpoints, event-dispatcher.md for new events)
• New clarity functions have corresponding PR in clarity-benchmarking repo
• New integration test(s) added to bitcoin-tests.yml

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (ee3afa5) 82.91% compared to head (8e9cf99) 82.96%.

Files	Patch %	Lines
...tackslib/src/chainstate/stacks/boot/pox_4_tests.rs	99.51%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             next    #4209      +/-   ##
==========================================
+ Coverage   82.91%   82.96%   +0.04%     
==========================================
  Files         429      429              
  Lines      302304   302748     +444     
==========================================
+ Hits       250650   251169     +519     
+ Misses      51654    51579      -75     

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[setzeus]

Looks like formatting failed in CI, have to run the following before committing:

cargo fmt --all -- --config group_imports=StdExternalCrate,imports_granularity=Module

[setzeus]

Some minimal comments/thoughts, really glad to see the work here!

Will go a long way to making PoX-related Rust tests easier / increasing code coverage for the rest of PoX-4 tasks.

[MarvinJanssen]

Strange, I have auto-formatting on. Must be a setting mismatch somewhere.

I'll tend to the changes as soon as possible.

Appreciate the quick review.

[jferrant]

Strange, I have auto-formatting on. Must be a setting mismatch somewhere.

I'll tend to the changes as soon as possible.

Appreciate the quick review.

Make sure you use cargo fmt-stacks in your auto settings as it has some additional flags to it that may change as the repo changes (so you don't have to update your auto fmting each time they do)

[moodmosaic]

Thank you, @MarvinJanssen!

The direction of this draft looks good. While I haven't pulled this locally yet, I wanted to initiate a discussion on potentially creating common abstractions to further streamline and condense the tests. I've left a detailed comment regarding this. Looking forward to your thoughts.

[MarvinJanssen]

Make sure you use cargo fmt-stacks in your auto settings as it has some additional flags to it that may change as the repo changes (so you don't have to update your auto fmting each time they do)

Yep I saw that, I had old settings in there. Thank you for the pointer!

[jcnelson]

Overall looks good but please address my comments first. Thanks!

[MarvinJanssen]

@wileyj this one is good to go I believe.

[jcnelson]

@wileyj I had asked to avoid merging this before reviewing

[AshtonStephens]

@wileyj I had asked to avoid merging this before reviewing

I don't think Jesse was in that discussion.

[wileyj]

@wileyj I had asked to avoid merging this before reviewing

ahh my mistake. was looking over the PR comments/approvals and it appeared good to go.