refactor: move tests folder structure and update pytest commands (#2785)

* refactor: move tests folder to src/backend

* chore(Makefile): update pytest commands to run tests from the correct directory paths for unit and integration tests

* refactor: update file path in test_custom_component.py

The file path in the test_custom_component.py file has been updated to use the correct relative path to the component_multiple_outputs.py file. This change ensures that the test code can access the correct file and improves the reliability of the test.

src/backend/tests/unit/text_experimental_components.py

@@ -0,0 +1,15 @@
+from langflow.components import prototypes
+
+
+def test_python_function_component():
+    # Arrange
+    python_function_component = prototypes.PythonFunctionComponent()
+
+    # Act
+    # function must be a string representation
+    function = "def function():\n    return 'Hello, World!'"
+    # result is the callable function
+    result = python_function_component.build(function)
+
+    # Assert
+    assert result() == "Hello, World!"