Add JUnit 5 ScorerExtension for AI model evaluation and associated library

- Implement `ScorerExtension` to inject and manage Scorer instances in tests.
- Support field and parameter injection for Scorer using `@ScorerConfiguration`.
- Add support for parameter injection of samples via `@SampleLocation` annotation.
- Provide built-in evaluation strategies:
  - `SemanticSimilarityStrategy` (cosine similarity-based evaluation).
  - `AiJudgeStrategy` (AI-powered evaluation with customizable prompts).
- Add tests for ScorerExtension:
  - Validate field and parameter injection of Scorer.
  - Test sample injection from YAML files.
  - Verify evaluation strategies and reporting.
- Document ScorerExtension:
  - Explain concepts: Scorer, Samples, Evaluation Strategies, Reports.
  - Usage examples for field/parameter injection and evaluation.
  - Guide for using built-in strategies and creating custom strategies.

Author: cescoffier

docs/modules/ROOT/nav.adoc

@@ -8,6 +8,7 @@
 ** xref:prompt-generation.adoc[Prompt Generation]
 ** xref:guardrails.adoc[Guardrails]
 ** xref:response-augmenter.adoc[Response Augmenter]
+** xref:testing.adoc[Testing]
 
 * LLMs
 ** xref:llms.adoc[LLMs]