fix: handle Pydantic V1/V2 compatibility in ChromaDBConfig

Fixes #4095

When users pass a chromadb.config.Settings object (Pydantic V1 model) to
ChromaDBConfig (Pydantic V2 dataclass), Pydantic V2 would attempt to
validate it and fail with: TypeError: BaseModel.validate() takes 2
positional arguments but 3 were given

This fix:
- Uses SkipValidation to prevent Pydantic V2 from validating the V1 Settings object
- Uses BeforeValidator to handle dict-to-Settings conversion
- Adds arbitrary_types_allowed=True to the config for extra safety

The settings field now accepts either:
- A chromadb.config.Settings instance (passed through unchanged)
- A dictionary of settings parameters (converted to Settings internally)

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

lib/crewai/tests/rag/chromadb/test_config.py

@@ -0,0 +1,130 @@
+"""Tests for ChromaDBConfig Pydantic V1/V2 compatibility."""
+
+import pytest
+from chromadb.config import Settings
+
+from crewai.rag.chromadb.config import ChromaDBConfig, _coerce_settings
+
+
+class TestCoerceSettings:
+    """Test suite for _coerce_settings validator function."""
+
+    def test_coerce_settings_passes_through_settings_instance(self):
+        """Test that existing Settings instances are passed through unchanged."""
+        settings = Settings(
+            persist_directory="./test_db",
+            allow_reset=True,
+            is_persistent=False,
+        )
+        result = _coerce_settings(settings)
+        assert result is settings
+        assert result.persist_directory == "./test_db"
+        assert result.allow_reset is True
+        assert result.is_persistent is False
+
+    def test_coerce_settings_converts_dict_to_settings(self):
+        """Test that dict inputs are converted to Settings instances."""
+        settings_dict = {
+            "persist_directory": "./my_custom_db",
+            "allow_reset": True,
+            "is_persistent": True,
+        }
+        result = _coerce_settings(settings_dict)
+        assert isinstance(result, Settings)
+        assert result.persist_directory == "./my_custom_db"
+        assert result.allow_reset is True
+        assert result.is_persistent is True
+
+    def test_coerce_settings_raises_type_error_for_invalid_input(self):
+        """Test that invalid input types raise TypeError."""
+        with pytest.raises(TypeError, match="settings must be a chromadb.config.Settings"):
+            _coerce_settings("invalid_string")
+
+        with pytest.raises(TypeError, match="settings must be a chromadb.config.Settings"):
+            _coerce_settings(123)
+
+        with pytest.raises(TypeError, match="settings must be a chromadb.config.Settings"):
+            _coerce_settings(["list", "of", "items"])
+
+
+class TestChromaDBConfigPydanticCompatibility:
+    """Test suite for ChromaDBConfig Pydantic V1/V2 compatibility.
+
+    These tests verify the fix for GitHub issue #4095:
+    Pydantic V1/V2 Compatibility Crash in RagTool when passing custom ChromaDB Settings.
+    """
+
+    def test_chromadb_config_accepts_settings_instance(self):
+        """Test that ChromaDBConfig accepts a chromadb.config.Settings instance.
+
+        This is the main regression test for issue #4095 where passing a Settings
+        instance would cause: TypeError: BaseModel.validate() takes 2 positional
+        arguments but 3 were given
+        """
+        custom_settings = Settings(
+            persist_directory="./my_db",
+            allow_reset=True,
+            is_persistent=False,
+        )
+        config = ChromaDBConfig(settings=custom_settings)
+
+        assert config.settings is custom_settings
+        assert config.settings.persist_directory == "./my_db"
+        assert config.settings.allow_reset is True
+        assert config.settings.is_persistent is False
+
+    def test_chromadb_config_accepts_settings_dict(self):
+        """Test that ChromaDBConfig accepts a dict for settings and converts it."""
+        settings_dict = {
+            "persist_directory": "./dict_db",
+            "allow_reset": False,
+            "is_persistent": True,
+        }
+        config = ChromaDBConfig(settings=settings_dict)
+
+        assert isinstance(config.settings, Settings)
+        assert config.settings.persist_directory == "./dict_db"
+        assert config.settings.allow_reset is False
+        assert config.settings.is_persistent is True
+
+    def test_chromadb_config_uses_default_settings_when_not_provided(self):
+        """Test that ChromaDBConfig uses default settings when none provided."""
+        config = ChromaDBConfig()
+
+        assert isinstance(config.settings, Settings)
+        assert config.settings.allow_reset is True
+        assert config.settings.is_persistent is True
+
+    def test_chromadb_config_with_all_parameters(self):
+        """Test ChromaDBConfig with all parameters including custom settings."""
+        custom_settings = Settings(
+            persist_directory="./full_test_db",
+            allow_reset=True,
+            is_persistent=True,
+        )
+        config = ChromaDBConfig(
+            tenant="test_tenant",
+            database="test_database",
+            settings=custom_settings,
+            limit=10,
+            score_threshold=0.8,
+            batch_size=50,
+        )
+
+        assert config.tenant == "test_tenant"
+        assert config.database == "test_database"
+        assert config.settings is custom_settings
+        assert config.limit == 10
+        assert config.score_threshold == 0.8
+        assert config.batch_size == 50
+
+    def test_chromadb_config_provider_is_chromadb(self):
+        """Test that provider field is always 'chromadb'."""
+        config = ChromaDBConfig()
+        assert config.provider == "chromadb"
+
+    def test_chromadb_config_is_frozen(self):
+        """Test that ChromaDBConfig is immutable (frozen)."""
+        config = ChromaDBConfig()
+        with pytest.raises(AttributeError):
+            config.tenant = "new_tenant"