Update template sensor to use async_track_template_result (#38940)

* Add template entity

* Update template tracking to work for template sensors

* add test for whitespace

* Update homeassistant/helpers/config_validation.py

* revert

* fix

* reduce

* fix _refresh missing decorator

* defer until start

* do not throw errors during startup

* defer tracking until start event

Co-authored-by: Swamp-Ig <github@ninjateaparty.com>

tests/helpers/test_config_validation.py

@@ -1092,3 +1092,24 @@ def test_script(caplog):
             cv.script_action(data)
 
         assert msg in str(excinfo.value)
+
+
+def test_whitespace():
+    """Test whitespace validation."""
+    schema = vol.Schema(cv.whitespace)
+
+    for value in (
+        None,
+        "" "T",
+        "negative",
+        "lock",
+        "tr  ue",
+        [],
+        [1, 2],
+        {"one": "two"},
+    ):
+        with pytest.raises(vol.MultipleInvalid):
+            schema(value)
+
+    for value in ("  ", "   "):
+        assert schema(value)