Added Controls testing + documentation

tests/controls/conftest.py

@@ -1,6 +1,6 @@
 import pytest
 
-from myfasthtml.core.instances import SingleInstance
+from myfasthtml.core.instances import SingleInstance, InstancesManager
 
 
 class RootInstanceForTests(SingleInstance):
@@ -25,4 +25,5 @@ def session():
 
 @pytest.fixture(scope="session")
 def root_instance(session):
+  InstancesManager.reset()
   return RootInstanceForTests(session=session)