Align SessionMock.getService with real behavior

[gnodet]

Summary

This PR brings SessionMock in line with the real Session implementation: getService(Class) now throws NoSuchElementException for unknown services by default.

It also simplifies the mock by centralizing the list of configured services and strengthens test coverage.

Motivation

• Previously, the mock returned null for unknown services (Mockito default), diverging from production behavior and occasionally masking test errors.
• The earlier “exclusion list” logic was verbose and fragile; adding a new configured service required editing a long chained predicate.

What changed

• Default behavior
  • Any service not explicitly configured in the mock now results in NoSuchElementException, matching AbstractSession semantics.
• Implementation simplification
  • Introduced a centralized CONFIGURED_SERVICES set and a contains check, replacing the chained predicate.
  • Used Mockito argThat to apply the default-throw behavior only for services not in CONFIGURED_SERVICES.
  • Resolved a minor circularity where setup could inadvertently query the mock during configuration.
• API & documentation
  • Deprecated getMockSessionWithEnhancedServiceBehavior(...); getMockSession(...) now has the enhanced behavior by default.
  • Updated Javadoc to document the default-throw behavior and the centralized configuration.
• Tests
  • Added tests to assert the default-throw behavior for unknown services and validate that configured services are wired correctly.

Compatibility

• Backward-compatible for typical usage:
  • Code/tests that request configured services continue to work.
  • Tests that relied on null for unknown services should now either configure/stub those services or expect NoSuchElementException.
• No production code changes; scope limited to impl/maven-testing and its tests.

Files touched

• impl/maven-testing/src/main/java/org/apache/maven/api/plugin/testing/stubs/SessionMock.java
• impl/maven-testing/src/test/java/org/apache/maven/api/plugin/testing/stubs/SessionGetServiceTest.java
• impl/maven-testing/src/test/java/org/apache/maven/api/plugin/testing/stubs/SessionMockDefaultBehaviorTest.java

Verification

• All existing tests pass locally; new tests cover the default-throw behavior and configured-service access.