fix: add missing name() method to WatsonEmbeddingFunction

Fixes #3597 - ChromaDB expects embedding functions to have a name() method
for validation. Added static method that returns 'watson' following the
same pattern as other embedding functions.

- Added comprehensive tests to verify the fix
- Ensures compatibility with ChromaDB validation requirements
- No regressions in existing Watson embedding functionality

Co-Authored-By: João <joao@crewai.com>

src/crewai/rag/embeddings/providers/ibm/embedding_callable.py

@@ -152,3 +152,8 @@ class WatsonEmbeddingFunction(EmbeddingFunction[Documents]):
         except Exception as e:
             print(f"Error during Watson embedding: {e}")
             raise
+
+    @staticmethod
+    def name() -> str:
+        """Return the name identifier for this embedding function."""
+        return "watson"