[Merged by Bors] - chore: Fix errors.As usage for PoetSvcUnstableError

[fasmat]

Motivation

errors.Is is generally used to compare returned errors to a concrete instance of an error like fs.ErrNotExists or io.EOF, while errors.As is used to assign generic errors to an instance of a specific type if needed.

Description

This removes the Is method from PoetSvcUnstableError and replaces usages of it with errors.As, which is already facilitated by the custom Unwrap method if needed.

This also removes the dummy instance ErrPoetServiceUnstable that primarily exists to assert that an error is of the type PoetSvcUnstableError.

Test Plan

• existing tests pass

TODO

• Explain motivation or link existing issue(s)
• Test changes and document test plan
• Update documentation as needed
• Update changelog as needed

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.0%. Comparing base (dc5fcaf) to head (42c7a19).

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #6217     +/-   ##
=========================================
- Coverage     82.0%   82.0%   -0.1%     
=========================================
  Files          308     308             
  Lines        33905   33906      +1     
=========================================
- Hits         27812   27807      -5     
- Misses        4318    4323      +5     
- Partials      1775    1776      +1     

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[fasmat]

bors merge

[spacemesh-bors]

Pull request successfully merged into develop.

Build succeeded:

• ci-status
• systest-status