4.x: Observable concatEager API reduction

[akarnokd]

Reduce API surface by introducing configuration record to various operators.

Observable

• concatEager + concatEagerDelayError -> concatEager + ObservableConcatEagerConfig
• concatArrayEager + concatArrayEagerDelayError -> concatArrayEager + ObservableConcatEagerConfig

Related: #8173

[github-actions]

🐷 TruffleHog + Entropy Beauty Scan

Average entropy of changed code: 4.735 bits/char
Verdict: ⚠️ Consider review — entropy outside sweet spot

Changed files entropy:

src/main/java/io/reactivex/rxjava4/core/Flowable.java: 4.779
src/main/java/io/reactivex/rxjava4/core/Observable.java: 4.757
src/main/java/io/reactivex/rxjava4/core/config/CompletableConcatConfig.java: 4.771
src/main/java/io/reactivex/rxjava4/core/config/CompletableMergeConfig.java: 4.849
src/main/java/io/reactivex/rxjava4/core/config/FlatMapConfig.java: 4.869
src/main/java/io/reactivex/rxjava4/core/config/GenericConfig.java: 4.848
src/main/java/io/reactivex/rxjava4/core/config/MaybeConcatEagerConfig.java: 4.797
src/main/java/io/reactivex/rxjava4/core/config/MaybeMergeConfig.java: 4.876
src/main/java/io/reactivex/rxjava4/core/config/ObservableCombineLatestConfig.java: 4.820
src/main/java/io/reactivex/rxjava4/core/config/ObservableMergeConfig.java: 4.884
src/main/java/io/reactivex/rxjava4/core/config/ParallelSchedulerConfig.java: 4.724
src/main/java/io/reactivex/rxjava4/core/config/SingleConcatConfig.java: 4.773
src/main/java/io/reactivex/rxjava4/core/config/SingleConcatEagerConfig.java: 4.794
src/main/java/io/reactivex/rxjava4/core/config/SingleMergeConfig.java: 4.869
src/main/java/io/reactivex/rxjava4/observers/TestObserver.java: 4.609
src/main/java/io/reactivex/rxjava4/schedulers/Schedulers.java: 4.730
src/main/java/io/reactivex/rxjava4/subscribers/TestSubscriber.java: 4.602
src/test/java/io/reactivex/rxjava4/core/config/ObservableMergeConfigTest.java: 4.986
src/test/java/io/reactivex/rxjava4/internal/operators/observable/ObservableDebounceTest.java: 4.750
src/test/java/io/reactivex/rxjava4/internal/operators/observable/ObservableFlatMapTest.java: 4.594

✅ No secrets or suspicious high-entropy strings found.

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

[github-actions]

🐷 TruffleHog + Entropy Beauty Scan

Average entropy of changed code: 4.735 bits/char
Verdict: ⚠️ Consider review — entropy outside sweet spot

Changed files entropy:

src/main/java/io/reactivex/rxjava4/core/Flowable.java: 4.779
src/main/java/io/reactivex/rxjava4/core/Observable.java: 4.757
src/main/java/io/reactivex/rxjava4/core/config/CompletableConcatConfig.java: 4.771
src/main/java/io/reactivex/rxjava4/core/config/CompletableMergeConfig.java: 4.849
src/main/java/io/reactivex/rxjava4/core/config/FlatMapConfig.java: 4.869
src/main/java/io/reactivex/rxjava4/core/config/GenericConfig.java: 4.848
src/main/java/io/reactivex/rxjava4/core/config/MaybeConcatEagerConfig.java: 4.797
src/main/java/io/reactivex/rxjava4/core/config/MaybeMergeConfig.java: 4.876
src/main/java/io/reactivex/rxjava4/core/config/ObservableCombineLatestConfig.java: 4.820
src/main/java/io/reactivex/rxjava4/core/config/ObservableMergeConfig.java: 4.884
src/main/java/io/reactivex/rxjava4/core/config/ParallelSchedulerConfig.java: 4.724
src/main/java/io/reactivex/rxjava4/core/config/SingleConcatConfig.java: 4.773
src/main/java/io/reactivex/rxjava4/core/config/SingleConcatEagerConfig.java: 4.794
src/main/java/io/reactivex/rxjava4/core/config/SingleMergeConfig.java: 4.869
src/main/java/io/reactivex/rxjava4/observers/TestObserver.java: 4.609
src/main/java/io/reactivex/rxjava4/schedulers/Schedulers.java: 4.730
src/main/java/io/reactivex/rxjava4/subscribers/TestSubscriber.java: 4.602
src/test/java/io/reactivex/rxjava4/core/config/ObservableMergeConfigTest.java: 4.986
src/test/java/io/reactivex/rxjava4/internal/operators/observable/ObservableDebounceTest.java: 4.750
src/test/java/io/reactivex/rxjava4/internal/operators/observable/ObservableFlatMapTest.java: 4.594

✅ 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 96.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 98.34%. Comparing base (f08aa83) to head (e01ad6f).
⚠️ Report is 1 commits behind head on 4.x.

Files with missing lines	Patch %	Lines
...ain/java/io/reactivex/rxjava4/core/Observable.java	94.11%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##                4.x    #8177   +/-   ##
=========================================
  Coverage     98.33%   98.34%           
- Complexity     6935     6938    +3     
=========================================
  Files           784      785    +1     
  Lines         48995    49013   +18     
  Branches       6596     6602    +6     
=========================================
+ Hits          48179    48201   +22     
+ Misses          624      620    -4     
  Partials        192      192           

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