Simplify visits reducers types with a status discriminator prop

[acelaya]

Part of #874

Replace the multiple boolean flags that determine the status of the visits and visits comparison reducers, with a single status discriminator prop that is less error prone and easier to reason about.

TODO

• Fix cancelling visits loading.
  EDIT: This stopped working because of a race condition in which status is set to canceled, but in-flight requests end up setting it back to loading. Previously, loading and canceled statuses were handled by two different flags, which incidentally worked around this race condition.

[codecov]

Codecov Report

❌ Patch coverage is 62.68657% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.83%. Comparing base (0012d20) to head (c3bca35).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/visits/helpers/VisitsLoadingFeedback.tsx	50.00%	0 Missing and 3 partials ⚠️
src/visits/reducers/nonOrphanVisits.ts	25.00%	2 Missing and 1 partial ⚠️
src/visits/reducers/orphanVisits.ts	25.00%	2 Missing and 1 partial ⚠️
...its/visits-comparison/ShortUrlVisitsComparison.tsx	75.00%	0 Missing and 2 partials ⚠️
src/visits/OrphanVisits.tsx	0.00%	0 Missing and 1 partial ⚠️
src/visits/ShortUrlVisitsHeader.tsx	0.00%	0 Missing and 1 partial ⚠️
src/visits/TagVisitsHeader.tsx	0.00%	0 Missing and 1 partial ⚠️
src/visits/VisitsStats.tsx	75.00%	0 Missing and 1 partial ⚠️
src/visits/reducers/common/createVisitsReducer.ts	90.90%	1 Missing ⚠️
src/visits/reducers/domainVisits.ts	50.00%	1 Missing ⚠️
... and 8 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #920      +/-   ##
==========================================
- Coverage   85.17%   84.83%   -0.35%     
==========================================
  Files         187      187              
  Lines        2807     2829      +22     
  Branches      361      379      +18     
==========================================
+ Hits         2391     2400       +9     
- Misses        120      124       +4     
- Partials      296      305       +9     

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