Fix fallback interval not causing new visits to be loaded

[acelaya]

The fallback interval was being tracked in a ref which was updated as a side effect. Since refs do not cause re-renders, the visits for the fallback interval were never loaded.

This PR changes the logic to update a piece of local state instead, which causes a re-render and makes the new visits to be loaded.

Updating local state as a side effect is not a great solution, but this component and how we handle the visits store needs a deeper refactoring to be able to solve this. This is a simple solution for now.

Closes #504

[codecov]

Codecov Report

Attention: Patch coverage is 37.50000% with 5 lines in your changes missing coverage. Please review.

Project coverage is 77.43%. Comparing base (db3e0d8) to head (79564d6).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/visits/VisitsStats.tsx	37.50%	1 Missing and 4 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #528   +/-   ##
=======================================
  Coverage   77.43%   77.43%           
=======================================
  Files         177      177           
  Lines        7237     7237           
  Branches     1501     1501           
=======================================
  Hits         5604     5604           
  Misses        162      162           
  Partials     1471     1471           

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