docs(fetch): correct the car_energy_reported_load check's docstrings (#5318 review)

minute_data() interpolates across a gap inside the history rather than
leaving it flat, so only a stretch before the history or padded over a
reset reads as no load; say so, and that a long outage over a charge can
still count. The load history is only emptied when car_charging_hold is
On as well. Give the test's nested load() helper a docstring.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: chalfontchubby

apps/predbat/fetch.py

@@ -3455,7 +3455,9 @@ def car_energy_exceeds_load_windows(self):
 
         The window in progress is left out: a cloud-polled load sensor can be many minutes behind the charger's, so it
         reads short there. A window with no load at all is skipped - a house always draws something, so a flat stretch
-        is the load sensor missing data (the history is padded, so missing minutes read as no increment), not evidence.
+        is missing data (before the history starts, or where minute_data() padded over a reset), not evidence. A gap
+        inside the history is not flat: minute_data() interpolates across it, so a load-sensor outage of some hours over
+        a charge spreads that charge thinly across the gap and can still count.
         """
         window = CAR_ENERGY_LOAD_CHECK_WINDOW
         lag = CAR_ENERGY_LOAD_CHECK_LAG
@@ -3482,7 +3484,8 @@ def check_car_energy_reported_load(self):
         from #5317). Warned once, and not again until no window shows it: the windows move with now, so a borderline count
         can dip below the threshold and back from one cycle to the next.
 
-        With the switch On, Predbat subtracts car_charging_energy from the load history and, for an Octopus Intelligent car
+        With the switch On, Predbat subtracts car_charging_energy from the load history (when car_charging_hold is also On,
+        the default) and, for an Octopus Intelligent car
         without a car_charging_now sensor, reads low house load as the car not charging. Against a load sensor that excludes
         the charger, the first empties the load history and the second cancels dispatches that are really charging.
         """

apps/predbat/tests/test_car_energy_reported_load.py

@@ -47,6 +47,9 @@ def _setup(my_predbat, load_includes_car, lag=0, sessions=((60, 180),), car_kw=C
     my_predbat.car_charging_energy = _incrementing(lambda minute: car_kw / 60 if _charging(minute, sessions) else 0.0, history)
 
     def load(minute):
+        """
+        The house load the load sensor saw in the minute that many minutes ago, with the car in it when it includes the charger.
+        """
         if load_gap and load_gap[0] <= minute < load_gap[1]:
             return 0.0
         car = car_kw if (load_includes_car and _charging(minute + lag, sessions)) else 0.0