chore: split functionality internally

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes 🛠 Tooling: Refactor large expect rule into granular pieces #116
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Splits out the roughly-not-specific-to-ESLint logic from the expect rule into:

• src/assertions: parsing assertions out from source code
• src/failures: determined unmatched/unmet assertions
• src/utils: miscellaneous helpers

[codecov]

Codecov Report

Attention: 188 lines in your changes are missing coverage. Please review.

Comparison is base (5dfdd92) 81.79% compared to head (291f2d5) 73.15%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
src/assertions/types.ts	0.00%	76 Missing ⚠️
src/utils/typescript.ts	46.72%	57 Missing ⚠️
src/failures/types.ts	0.00%	21 Missing ⚠️
src/rules/expect.ts	80.00%	18 Missing ⚠️
src/assertions/parseAssertions.ts	90.44%	13 Missing ⚠️
src/failures/getExpectTypeFailures.ts	97.14%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #117      +/-   ##
==========================================
- Coverage   81.79%   73.15%   -8.65%     
==========================================
  Files          10       16       +6     
  Lines         835      946     +111     
  Branches       93       85       -8     
==========================================
+ Hits          683      692       +9     
- Misses        152      254     +102     

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[JoshuaKGoldberg]

@danvk adding you since we're talking soon - if you have time, thought you might enjoy discussing the refactor 😄

[JoshuaKGoldberg]

Ah, this is blocking me working on more parts of the plugin. I'm going to merge now - but let me know if there's anything you think I could have done better here!