4.x: Single API reduction: concat & concatEager

[akarnokd]

Simplify API by changing the number of overloads of various operators.

Single

• concat and concatDelayError -> concat with SingleConcatConfig configuration record.
• concatArray and concatArrayDelayError -> concatArray with SingleConcatConfig configuration record.
• concatEager and concatEagerDelayError -> concatEager with SingleConcatEagerConfig configuration record.
• concatArrayEager and concatArrayEagerDelayError -> concatArrayEager with SingleConcatEagerConfig configuration record.

Related: #8173

[github-actions]

🐷 TruffleHog + Entropy Beauty Scan

Average entropy of changed code: 4.791 bits/char
Verdict: ⚠️ Consider review — entropy outside sweet spot

Changed files entropy:

src/main/java/io/reactivex/rxjava4/core/Completable.java: 4.835
src/main/java/io/reactivex/rxjava4/core/config/CompletableConcatConfig.java: 4.760
src/main/java/io/reactivex/rxjava4/core/config/CompletableMergeConfig.java: 4.840
src/test/java/io/reactivex/rxjava4/completable/CompletableTest.java: 4.630
src/test/java/io/reactivex/rxjava4/core/config/CompletableConcatConfigTest.java: 4.969
src/test/java/io/reactivex/rxjava4/core/config/CompletableMergeConfigTest.java: 4.992
src/test/java/io/reactivex/rxjava4/internal/operators/completable/CompletableConcatArrayDelayErrorTest.java: 4.882
src/test/java/io/reactivex/rxjava4/internal/operators/completable/CompletableConcatDelayErrorTest.java: 4.731
src/test/java/io/reactivex/rxjava4/internal/operators/completable/CompletableConcatTest.java: 4.596
src/test/java/io/reactivex/rxjava4/internal/operators/completable/CompletableMergeTest.java: 4.628
src/test/java/io/reactivex/rxjava4/validators/ParamValidationCheckerTest.java: 4.833

✅ 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: 4.791 bits/char
Verdict: ⚠️ Consider review — entropy outside sweet spot

Changed files entropy:

src/main/java/io/reactivex/rxjava4/core/Completable.java: 4.835
src/main/java/io/reactivex/rxjava4/core/config/CompletableConcatConfig.java: 4.760
src/main/java/io/reactivex/rxjava4/core/config/CompletableMergeConfig.java: 4.840
src/test/java/io/reactivex/rxjava4/completable/CompletableTest.java: 4.630
src/test/java/io/reactivex/rxjava4/core/config/CompletableConcatConfigTest.java: 4.969
src/test/java/io/reactivex/rxjava4/core/config/CompletableMergeConfigTest.java: 4.992
src/test/java/io/reactivex/rxjava4/internal/operators/completable/CompletableConcatArrayDelayErrorTest.java: 4.882
src/test/java/io/reactivex/rxjava4/internal/operators/completable/CompletableConcatDelayErrorTest.java: 4.731
src/test/java/io/reactivex/rxjava4/internal/operators/completable/CompletableConcatTest.java: 4.596
src/test/java/io/reactivex/rxjava4/internal/operators/completable/CompletableMergeTest.java: 4.628
src/test/java/io/reactivex/rxjava4/validators/ParamValidationCheckerTest.java: 4.833

✅ 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 98.31%. Comparing base (4d8e19d) to head (7707b42).

Additional details and impacted files

@@             Coverage Diff              @@
##                4.x    #8167      +/-   ##
============================================
- Coverage     98.36%   98.31%   -0.05%     
- Complexity     6943     6944       +1     
============================================
  Files           775      777       +2     
  Lines         49023    49056      +33     
  Branches       6591     6595       +4     
============================================
+ Hits          48221    48231      +10     
- Misses          620      627       +7     
- Partials        182      198      +16     

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