feat: Add comprehensive integration test coverage

- Add 18 new integration test suites covering advanced SDK features
- Add utility classes for test helpers and performance assertions
- Optimize test execution with parallel processing
- Update Credentials management for better security

Test suites include coverage for:
- Complex query scenarios (AND/OR/NOT operations)
- Deep reference fetching and nested structures
- JSON RTE with embedded items
- Modular blocks and global fields
- Locale fallback mechanisms
- Field projection and pagination
- Asset management operations
- Error handling and retry logic
- Sync operations and metadata

All tests passing with optimized execution time.

.gitignore

@@ -272,3 +272,4 @@ src/main/resources/
 /src/main/java/com/contentstack/sdk/models/
 /.vscode/
 /.vscode/
+/docs/

pom.xml

@@ -282,8 +282,34 @@
                         <include>**/*IT.java</include>
                     </includes>
                     <skipTests>true</skipTests>
+                    <!-- OPTIMIZED: Parallel execution with controlled concurrency -->
+                    <parallel>classes</parallel>
+                    <threadCount>4</threadCount>
+                    <perCoreThreadCount>false</perCoreThreadCount>
+                    <useUnlimitedThreads>false</useUnlimitedThreads>
+                    <!-- Reuse forks for better performance -->
+                    <reuseForks>true</reuseForks>
+                    <forkCount>2</forkCount>
+                    <!-- Increase timeout for slow tests -->
+                    <forkedProcessTimeoutInSeconds>500</forkedProcessTimeoutInSeconds>
+                    <!-- Better memory management -->
+                    <argLine>-Xmx2048m -XX:MaxMetaspaceSize=512m</argLine>
                 </configuration>
             </plugin>
+
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-report-plugin</artifactId>
+                <version>2.22.2</version>
+                <executions>
+                    <execution>
+                        <phase>test</phase>
+                        <goals>
+                            <goal>report-only</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
 
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>