feat: rag configuration with optional dependency support (#3394)

### RAG Config System

* Added ChromaDB client creation via config with sensible defaults
* Introduced optional imports and shared RAG config utilities/schema
* Enabled embedding function support with ChromaDB provider integration
* Refactored configs for immutability and stronger type safety
* Removed unused code and expanded test coverage

tests/rag/config/test_factory.py

@@ -0,0 +1,34 @@
+"""Tests for RAG config factory."""
+
+from unittest.mock import Mock, patch
+
+from crewai.rag.config.factory import create_client
+
+
+def test_create_client_chromadb():
+    """Test ChromaDB client creation."""
+    mock_config = Mock()
+    mock_config.provider = "chromadb"
+
+    with patch("crewai.rag.config.factory.require") as mock_require:
+        mock_module = Mock()
+        mock_client = Mock()
+        mock_module.create_client.return_value = mock_client
+        mock_require.return_value = mock_module
+
+        result = create_client(mock_config)
+
+        assert result == mock_client
+        mock_require.assert_called_once_with(
+            "crewai.rag.chromadb.factory", purpose="The 'chromadb' provider"
+        )
+        mock_module.create_client.assert_called_once_with(mock_config)
+
+
+def test_create_client_unsupported_provider():
+    """Test unsupported provider returns None for now."""
+    mock_config = Mock()
+    mock_config.provider = "unsupported"
+
+    result = create_client(mock_config)
+    assert result is None

tests/rag/config/test_optional_imports.py

@@ -0,0 +1,22 @@
+"""Tests for optional imports."""
+
+import pytest
+
+from crewai.rag.config.optional_imports.base import _MissingProvider
+from crewai.rag.config.optional_imports.providers import MissingChromaDBConfig
+
+
+def test_missing_provider_raises_runtime_error():
+    """Test that _MissingProvider raises RuntimeError on instantiation."""
+    with pytest.raises(
+        RuntimeError, match="provider '__missing__' requested but not installed"
+    ):
+        _MissingProvider()
+
+
+def test_missing_chromadb_config_raises_runtime_error():
+    """Test that MissingChromaDBConfig raises RuntimeError on instantiation."""
+    with pytest.raises(
+        RuntimeError, match="provider 'chromadb' requested but not installed"
+    ):
+        MissingChromaDBConfig()