4.x: Streamable + takeUntil + groupBy + refactor + helpers

[akarnokd]

Implement more Streamable operators:

• takeUntil(Streamable other)
• groupBy(Function)

Improve test infrastructure

• TestSubscriber.errors() / TestObserver.errors()
• TestSubscriber.toString() / TestObserver.toString()

API refactor

Move ConnectableObservable, GroupedObservable, ConnectableFlowable and GroupedFlowable into io.reactivex.rxjava4.core package from their respective 2 x **.observables and **.flowables packages.

[github-actions]

🐷 TruffleHog + Entropy Beauty Scan

Average entropy of changed code: 4.71 bits/char
Verdict: ⚠️ Consider review — entropy outside sweet spot

Changed files entropy:

src/main/java/io/reactivex/rxjava4/core/Completable.java: 4.834
src/main/java/io/reactivex/rxjava4/core/Maybe.java: 4.842
src/main/java/io/reactivex/rxjava4/core/Single.java: 4.831
src/main/java/io/reactivex/rxjava4/core/Streamable.java: 4.656
src/main/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableForEach.java: 4.377
src/main/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableFromCompletable.java: 4.749
src/main/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableFromMaybe.java: 4.706
src/main/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableFromSingle.java: 4.720
src/main/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableTakeWhile.java: 4.695
src/main/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableToObservable.java: 4.440
src/main/java/io/reactivex/rxjava4/internal/util/ExceptionHelper.java: 4.526
src/test/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableBaseTest.java: 4.792
src/test/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableFromCompletableTest.java: 4.820
src/test/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableFromMaybeTest.java: 4.818
src/test/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableFromSingleTest.java: 4.832
src/test/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableLifecycleVerifier.java: 4.794
src/test/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableLifecycleVerifierTest.java: 4.931
src/test/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableTakeWhileTest.java: 4.774
src/test/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableToObservableTest.java: 4.773
src/test/java/io/reactivex/rxjava4/internal/util/ExceptionHelperTest.java: 4.824

✅ No secrets or suspicious high-entropy strings found.

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

[codecov]

Codecov Report

❌ Patch coverage is 97.18876% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.68%. Comparing base (31cddef) to head (2c00fa1).

Files with missing lines	Patch %	Lines
...ternal/operators/streamable/StreamableGroupBy.java	96.55%	1 Missing and 3 partials ⚠️
.../internal/operators/streamable/StageResumable.java	88.23%	0 Missing and 2 partials ⚠️
...nternal/operators/streamable/StreamableHelper.java	98.52%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                4.x    #8215      +/-   ##
============================================
- Coverage     98.70%   98.68%   -0.03%     
- Complexity     6955     7000      +45     
============================================
  Files           799      804       +5     
  Lines         49174    49412     +238     
  Branches       6646     6674      +28     
============================================
+ Hits          48538    48763     +225     
- Misses          445      450       +5     
- Partials        191      199       +8     

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[github-actions]

🐷 TruffleHog + Entropy Beauty Scan

Average entropy of changed code: 4.71 bits/char
Verdict: ⚠️ Consider review — entropy outside sweet spot

Changed files entropy:

src/main/java/io/reactivex/rxjava4/core/Completable.java: 4.834
src/main/java/io/reactivex/rxjava4/core/Maybe.java: 4.842
src/main/java/io/reactivex/rxjava4/core/Single.java: 4.831
src/main/java/io/reactivex/rxjava4/core/Streamable.java: 4.656
src/main/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableForEach.java: 4.377
src/main/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableFromCompletable.java: 4.749
src/main/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableFromMaybe.java: 4.706
src/main/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableFromSingle.java: 4.720
src/main/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableTakeWhile.java: 4.695
src/main/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableToObservable.java: 4.440
src/main/java/io/reactivex/rxjava4/internal/util/ExceptionHelper.java: 4.526
src/test/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableBaseTest.java: 4.792
src/test/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableFromCompletableTest.java: 4.820
src/test/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableFromMaybeTest.java: 4.818
src/test/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableFromSingleTest.java: 4.832
src/test/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableLifecycleVerifier.java: 4.794
src/test/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableLifecycleVerifierTest.java: 4.931
src/test/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableTakeWhileTest.java: 4.774
src/test/java/io/reactivex/rxjava4/internal/operators/streamable/StreamableToObservableTest.java: 4.773
src/test/java/io/reactivex/rxjava4/internal/util/ExceptionHelperTest.java: 4.824

✅ No secrets or suspicious high-entropy strings found.

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