test(storage): exclude jqwik tests on Java 8

[nnicolee]

Problem

Jqwik version 1.9+ requires JDK 11+ at runtime. Since google-cloud-java runs tests on JDK 8 matrix environments, Jqwik's reflection-based class scanning fails when JSpecify 1.0.0 annotations are present, causing UnsupportedClassVersionError or reflection scanner crashes during JUnit test discovery on Java 8.

Solution

This PR introduces a clean profile-based exclusion to isolate Jqwik on Java 8 without impacting modern Java environments:

1. Moved Jqwik dependency into jqwik-tests profile: The net.jqwik:jqwik library is no longer loaded globally; it is only added to the test classpath on JDK 11+ ([11,)).
2. Added exclude-jqwik-on-java8 profile: Active only when the JDK is exactly 1.8.
3. Excluded Jqwik test compilation: Inside the Java 8 profile, we use testExcludes to skip compiling all Jqwik-based property tests (e.g., *PropertyTest.java, jqwik packages, etc.) to prevent compile errors when Jqwik is not on the classpath.
4. Decoupled compilation dependencies: Excluded RewindableByteBufferContentTest.java on Java 8 as well, since it has an import reference to a nested class inside RewindableContentPropertyTest.java and would otherwise pull it into compiler scope.

Rationale

• Decouples Jqwik testing dependencies on Java 8 matrix builds, preventing pipeline failures.
• Retains 100% test coverage for these property-based tests on modern JDKs (11, 17, 21, etc.) since matrix builds continue to compile and run them normally.

[gemini-code-assist]

Code Review

This pull request modifies the Maven configuration to conditionally load the jqwik dependency on JDK 11+ and exclude specific test files when compiling on Java 8. The review feedback points out that hardcoding individual test files in the exclusion list is fragile and risks losing standard JUnit test coverage on Java 8. It is recommended to separate jqwik property tests into dedicated files or packages to simplify the POM exclusions to wildcard patterns.

[gemini-code-assist]

Hardcoding individual test files in the POM's exclusion list is fragile and difficult to maintain. Additionally, if these files contain standard JUnit tests alongside jqwik property tests, excluding the entire file from compilation on Java 8 means we completely lose standard test coverage on Java 8.

Recommendation

1. Separate Test Concerns: Move jqwik property tests into dedicated files ending with PropertyTest.java (e.g., JsonUtilsPropertyTest.java) or place them under a jqwik package.
2. Retain Java 8 Coverage: Keep standard JUnit tests in their original files (e.g., JsonUtilsTest.java) without any jqwik imports so they can compile and run on Java 8.
3. Simplify POM: This allows you to simplify the exclusions here to just the wildcard patterns (**/*PropertyTest.java and **/jqwik/**), removing the need to list individual files.