Update maven-extension module to follow style guide

[Copilot]

This PR updates the maven-extension module to comply with the style guide requirements outlined in docs/style-guide.md.

Changes Made

@autoservice Migration

• Added @AutoService annotations to all SPI implementations:
  • MavenResourceProvider (implements ResourceProvider)
  • MavenResourceDetector (implements ComponentProvider<Resource>)
  • All MojoGoalExecutionHandler implementations (GoogleJibBuildHandler, MavenDeployHandler, SnykMonitorHandler, SnykTestHandler, SpringBootBuildImageHandler)
• Removed all manual META-INF/services files as they are now auto-generated by @AutoService
• Updated MojoGoalExecutionHandlerConfiguration to rely solely on ServiceLoader instead of manual handler instantiation
• Made handler classes public as required by ServiceLoader

Test Visibility Updates

• Updated all test classes from public to package-protected visibility
• Updated all test methods from public to package-protected visibility

Dependency Updates

• Added com.google.auto.service:auto-service as annotationProcessor, compileOnly, and testImplementation dependency

Benefits

This change modernizes the SPI registration approach by:

• Eliminating the need to manually maintain META-INF/services files
• Reducing the risk of mismatched service files and implementations
• Following established OpenTelemetry Java Contrib conventions used in other modules
• Improving maintainability by automatically generating service registrations at compile time

All existing functionality is preserved while the code now follows the project's style guide requirements.

Fixes #163.

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[trask]

@copilot why this change?

[Copilot]

The changes on lines 36-37 implement the style guide requirements for SPI registration:

1. Line 36: Added @AutoService(MojoGoalExecutionHandler.class) to automatically generate the META-INF/services file, eliminating manual service file maintenance
2. Line 37: Changed from final class to public final class because ServiceLoader requires implementation classes to be public for instantiation

This follows the established pattern used throughout the OpenTelemetry Java Contrib codebase and modernizes the SPI registration approach as outlined in the style guide.

[trask]

@copilot why this change?

[Copilot]

The changes on lines 19-21 implement the style guide requirements for SPI registration:

1. Line 8: Added import com.google.auto.service.AutoService;
2. Line 20: Added @AutoService(MojoGoalExecutionHandler.class) to automatically generate the META-INF/services file, eliminating manual service file maintenance
3. Line 21: Changed from final class to public final class because ServiceLoader requires implementation classes to be public for instantiation

This follows the same pattern applied to all other MojoGoalExecutionHandler implementations and modernizes the SPI registration approach as outlined in the style guide.

[trask]

@copilot why this change

[Copilot]

The changes on lines 19-21 implement the style guide requirements for SPI registration:

1. Line 8: Added import com.google.auto.service.AutoService;
2. Line 20: Added @AutoService(MojoGoalExecutionHandler.class) to automatically generate the META-INF/services file, eliminating manual service file maintenance
3. Line 21: Changed from final class to public final class because ServiceLoader requires implementation classes to be public for instantiation

This follows the same pattern applied to all other MojoGoalExecutionHandler implementations and modernizes the SPI registration approach as outlined in the style guide.