Add CachingLocator.

[ericsnowcurrently]

Note that I factored out the BackgroundRequestLooper class to keep CachingLocator focused, especially as I found it was important to deal with one "refresh" at a time.

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR).
• Title summarizes what is changing.
• [ ] Has a news entry file (remember to thank yourself!).
• Appropriate comments and documentation strings in the code.
• Has sufficient logging.
• [ ] Has telemetry for enhancements.
• Unit tests & system/integration tests are added/updated.
• [ ] Test plan is updated as appropriate.
• [ ] package-lock.json has been regenerated by running npm install (if dependencies have changed).
• [ ] The wiki is updated with any design decisions/details.

[codecov-commenter]

Codecov Report

Merging #14020 into main will increase coverage by 0.07%.
The diff coverage is 64.46%.

@@            Coverage Diff             @@
##             main   #14020      +/-   ##
==========================================
+ Coverage   59.96%   60.04%   +0.07%     
==========================================
  Files         706      710       +4     
  Lines       39180    39420     +240     
  Branches     5681     5708      +27     
==========================================
+ Hits        23494    23668     +174     
- Misses      14449    14501      +52     
- Partials     1237     1251      +14     

Impacted Files	Coverage Δ
src/client/pythonEnvironments/index.ts	17.64% <21.42%> (+0.57%)	⬆️
...ronments/base/locators/composite/cachingLocator.ts	64.88% <64.88%> (ø)
src/client/pythonEnvironments/base/envsCache.ts	92.59% <100.00%> (+8.59%)	⬆️
...onments/base/locators/composite/reducingLocator.ts	100.00% <100.00%> (ø)
src/client/common/utils/platform.ts	68.00% <0.00%> (-4.00%)	⬇️
...discovery/locators/services/windowsStoreLocator.ts	100.00% <0.00%> (ø)
src/client/pythonEnvironments/common/posixUtils.ts	91.66% <0.00%> (ø)
...covery/locators/services/posixKnownPathsLocator.ts	100.00% <0.00%> (ø)
... and 2 more

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[ericsnowcurrently]

@kimadeline and @karrtikr, I should have left this as a draft PR. I'll let you know when I've wrapped up the last few changes I have to make.

[ericsnowcurrently]

@kimadeline, @karrtikr, the PR is ready to go now.

[kimadeline]

Since Kartik is out, you may want to request a review from @karthiknadig, because I don't want to shoulder the responsibility of reviewing this PR alone 😆

[karrtikr]

@ericsnowcurrently @kimadeline I just had one comment regarding potential correctness #14020 (comment) I leave the rest upto you guys😄

[kimadeline]

Will re-review this afternoon.

[ericsnowcurrently]

resetting "checks" trigger

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities (and 0 Security Hotspots to review)
0 Code Smells

No Coverage information
0.0% Duplication

[codecov-io]

Codecov Report

Merging #14020 into main will decrease coverage by 0.00%.
The diff coverage is 64.17%.

@@            Coverage Diff             @@
##             main   #14020      +/-   ##
==========================================
- Coverage   59.91%   59.91%   -0.01%     
==========================================
  Files         709      712       +3     
  Lines       39334    39520     +186     
  Branches     5698     5722      +24     
==========================================
+ Hits        23567    23678     +111     
- Misses      14529    14586      +57     
- Partials     1238     1256      +18     

Impacted Files	Coverage Δ
src/client/pythonEnvironments/index.ts	17.64% <21.42%> (+0.57%)	⬆️
src/client/common/utils/backgroundLoop.ts	60.71% <60.71%> (ø)
...ronments/base/locators/composite/cachingLocator.ts	70.45% <70.45%> (ø)
src/client/pythonEnvironments/base/envsCache.ts	85.18% <84.61%> (+1.18%)	⬆️
...onments/base/locators/composite/reducingLocator.ts	100.00% <100.00%> (ø)
...very/locators/services/virtualenvwrapperLocator.ts	76.92% <0.00%> (-15.39%)	⬇️
src/client/common/utils/platform.ts	60.00% <0.00%> (-12.00%)	⬇️
.../pythonEnvironments/common/externalDependencies.ts	64.10% <0.00%> (-2.57%)	⬇️
src/client/linters/pydocstyle.ts	86.66% <0.00%> (-2.23%)	⬇️
src/client/datascience/debugLocationTracker.ts	76.56% <0.00%> (-1.57%)	⬇️
... and 5 more

---

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