[core] Assert stateless capture in test, fix TemplatableFn comment

esphome/cpp_generator.py

@@ -845,7 +845,7 @@ async def templatable(
         if output_type is std_string:
             return FlashStringLiteral(value)
     # For non-string types, wrap constants in stateless lambdas so that
-    # TemplatableValue stores them as function pointers (4 bytes vs 8).
+    # TemplatableFn (used by TEMPLATABLE_VALUE macro) stores them as function pointers.
     if output_type is not None:
         from esphome.cpp_types import std_string
 

tests/unit_tests/test_cpp_generator.py

@@ -673,6 +673,7 @@ async def test_templatable__string_with_non_string_output_type() -> None:
     result = await cg.templatable("hello", [], ct.bool_)
 
     assert isinstance(result, cg.LambdaExpression)
+    assert result.capture == ""
 
 
 @pytest.mark.asyncio