Align build to Java 11, add test suite + CI, and code-quality fixes

[devin-ai-integration]

Summary

Build/config alignment, a real test suite, code-quality cleanups, README fixes, and a CI workflow.

Java version decision (Phase 1): The 2nd-edition examples use APIs added after Java 8 — Optional.or, Optional.stream (chap10), Collectors.flatMapping/filtering (chap6), Stream.takeWhile (chap6). So targeting Java 8 fails to compile. Rather than rewrite pedagogical book code, the project now targets Java 11 (modern LTS), consistent across pom.xml, README.md, and CI.

Phase 1 — build/config (pom.xml)

 <properties>
+  <maven.compiler.release>11</maven.compiler.release>   # was <source>1.9</source>/<target>1.9</target>
+  <jmh.version>1.37</jmh.version>                        # was 1.17.4
 </properties>
- maven-compiler-plugin 3.1                               → 3.13.0 (supports <release>)
- maven-shade-plugin    (no version)                      → 3.5.3 (pinned/reproducible)
- junit 4.11                                              → 4.13.2, scope=test

Phase 2 — testing structure

• Created src/test/java root.
• Relocated the misplaced test: src/main/.../chap10/ReadPositiveIntParam.java had a @Test under src/main (never run by Surefire). The example helpers (readDurationImperative, readDurationWithOptional, s2i) stay in src/main; the test moved to src/test/.../chap10/ReadPositiveIntParamTest.java.
• Added real tests: FilteringApplesTest (chap1) and UtilTest (chap11). 6 tests total, all passing.

Phase 3 — code quality (chap11/Util.java, chap1/FilteringApples.java)

- return new Double(formatter.format(number));          // deprecated ctor
+ return Double.parseDouble(formatter.format(number));

• Removed the large commented-out allOf-based sequence alternative.
• Stripped trailing whitespace in chap1/FilteringApples.java.

Phase 4 — README

• Replaced dead Oracle java8-2100321.html and jdk8.java.net links with Adoptium/Oracle download links.
• Fixed typo: "Reduntant" → "Redundant".
• Java version guidance now matches the pom.xml (Java 11) decision.

Phase 5 — CI

• Added .github/workflows/build.yml: sets up Temurin JDK 11, runs mvn compile then mvn test on push/PR to master.
• .gitignore: un-ignored .github (previously caught by /.*) and ignored the shade-generated dependency-reduced-pom.xml.

Per the task note, intentionally duplicated per-chapter domain models (e.g. Dish, Apple) were left untouched.

Verified locally: mvn clean verify on JDK 11 → BUILD SUCCESS, 6/6 tests pass, shaded benchmarks.jar produced.

Link to Devin session: https://app.devin.ai/sessions/4a09706b288c4fdabc01517620676128
Requested by: @bnob-git

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