test(storage): exclude jqwik tests on Java 8 (#13846)

### 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.

Author: nnicolee

java-storage/google-cloud-storage/pom.xml

@@ -338,12 +338,6 @@
       <artifactId>junit-vintage-engine</artifactId>
       <scope>test</scope>
     </dependency>
-    <dependency>
-      <groupId>net.jqwik</groupId>
-      <artifactId>jqwik</artifactId>
-      <version>1.9.3</version>
-      <scope>test</scope>
-    </dependency>
     <dependency>
       <groupId>io.github.classgraph</groupId>
       <artifactId>classgraph</artifactId>
@@ -474,6 +468,60 @@
   </build>
 
   <profiles>
+    <profile>
+      <id>jqwik-tests</id>
+      <activation>
+        <jdk>[11,)</jdk>
+      </activation>
+      <dependencies>
+        <dependency>
+          <groupId>net.jqwik</groupId>
+          <artifactId>jqwik</artifactId>
+          <version>1.9.3</version>
+          <scope>test</scope>
+        </dependency>
+      </dependencies>
+    </profile>
+    <!--
+      Exclude Jqwik and its tests on Java 8 because Jqwik 1.9+ requires Java 11+.
+      Jqwik's reflection-based test scanning fails on Java 8 when JSpecify annotations are present.
+      Test coverage for these Jqwik property tests is still run and maintained on JDK 11+ matrix builds.
+    -->
+    <profile>
+      <id>exclude-jqwik-on-java8</id>
+      <activation>
+        <jdk>1.8</jdk>
+      </activation>
+      <build>
+        <plugins>
+          <plugin>
+            <groupId>org.apache.maven.plugins</groupId>
+            <artifactId>maven-compiler-plugin</artifactId>
+            <executions>
+              <execution>
+                <id>default-testCompile</id>
+                <configuration>
+                  <testExcludes>
+                    <exclude>**/*PropertyTest.java</exclude>
+                    <exclude>**/JqwikTest.java</exclude>
+                    <exclude>**/jqwik/**</exclude>
+                    <exclude>**/StorageV2ProtoUtilsTest.java</exclude>
+                    <exclude>**/JsonUtilsTest.java</exclude>
+                    <exclude>**/ChunkSegmenterTest.java</exclude>
+                    <exclude>**/DefaultBufferedWritableByteChannelTest.java</exclude>
+                    <exclude>**/MinFlushBufferedWritableByteChannelTest.java</exclude>
+                    <exclude>**/DefaultBufferedReadableByteChannelTest.java</exclude>
+                    <exclude>**/Crc32cValueTest.java</exclude>
+                    <exclude>**/ITSyncingFileChannelTest.java</exclude>
+                    <exclude>**/RewindableByteBufferContentTest.java</exclude>
+                  </testExcludes>
+                </configuration>
+              </execution>
+            </executions>
+          </plugin>
+        </plugins>
+      </build>
+    </profile>
     <profile>
       <id>idea-jqwik</id>
       <dependencies>