4.x: Add VirtualSchedulerTests extends AbstractSchedulerConcurrencyTests

[akarnokd]

Verify the virtual scheduler via the test suite for schedulers.

[github-actions]

🐷 TruffleHog + Entropy Beauty Scan

Average entropy of changed code: 4.611 bits/char
Verdict: ✅ Mid-4 beauty detected (thoughtful human code!)

Changed files entropy:

build.gradle: 5.009
src/test/java/io/reactivex/rxjava4/core/RxJavaSelfTest.java: 4.701
src/test/java/io/reactivex/rxjava4/core/RxJavaTest.java: 4.620
src/test/java/io/reactivex/rxjava4/core/XFlatMapTest.java: 4.114

✅ No secrets or suspicious high-entropy strings found.

Mid-4 beauty heuristic in action — powered by our entropy chats! 😊

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.34%. Comparing base (c357f75) to head (d00666c).

Additional details and impacted files

@@             Coverage Diff              @@
##                4.x    #8204      +/-   ##
============================================
+ Coverage     98.33%   98.34%   +0.01%     
+ Complexity     6785     6783       -2     
============================================
  Files           777      777              
  Lines         48506    48506              
  Branches       6570     6570              
============================================
+ Hits          47696    47703       +7     
+ Misses          610      606       -4     
+ Partials        200      197       -3     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.