refactor(warnings): rework MiscalledStubWarning checker for clarity

[mcous]

#204 raised a couple questions about when Decoy chooses to emit errors and warnings, one of which is addressed by #218. The second question asks:

[Should Decoy complain if] we try calling a method that is part of the mocked spec which is not mocked?

Currently, Decoy will not complain in this scenario. It will issue a MiscalledStubWarning if and only if the mock in question is used at least once with decoy.when, which acts as a marker for a test to say "I care about this dependency". This PR comes out of an investigation into the feasibility of enabling a MiscalledStubWarning even if the mock is fully unconfigured. In the course of answering this question:

• I reworked this portion of the warning checker
• I decided the answer is still no

Issuing a warning in this case forces every test using given subject to decoy.when or decoy.verify every single dependency the subject uses, even if a particular test isn't concerned with that behavior. In Decoy's own test suite this would trigger 8 warnings, and "fixing" those warnings would bloat the tests in question without providing meaningful design feedback

[mcous]

Current dependencies on/for this PR:

• main
  • PR chore: upgrade docs dependencies and fix warnings #217
    • PR feat(spy): warn if mock used with a missing attribute #218
      • PR refactor(warnings): rework MiscalledStubWarning checker for clarity #219 👈

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[codecov]

Codecov Report

Merging #219 (fe9edf9) into main (72cefe4) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #219      +/-   ##
==========================================
+ Coverage   98.37%   98.38%   +0.01%     
==========================================
  Files          19       19              
  Lines         739      744       +5     
  Branches       88       90       +2     
==========================================
+ Hits          727      732       +5     
  Misses         10       10              
  Partials        2        2              

Files Changed	Coverage Δ
decoy/warning_checker.py	100.00% <100.00%> (ø)
decoy/warnings.py	100.00% <100.00%> (ø)