Apply PR #144 review round 3: lifecycle tests for malformed-option fallback, comment/test hygiene

Add LIFECYCLE tests that wire an entry via make_entry(options=...) and
call async_setup_entry, covering the from_options_resilient fallback
production actually uses (P2): a fully malformed options dict
(horizon_days=True, day_rollover_time='99:99',
morning_summary_time='25:00') succeeds with the day-rollover listener
at the default 00:00 and the backfill over DEFAULT_HORIZON_DAYS; and a
bad sibling (horizon_days=5, morning_summary_time='25:00') keeps
horizon_days == 5. Swapping from_options_resilient for from_options in
setup now fails these tests.

Reword comments/tests describing review history rather than the code:
__init__.py setup comment, test_core_settings P2-3/P2-1/P2-5 markers,
the moved from_options horizon test, and the AST scanner docstrings.

Test hygiene: move freeze_nestquest_clock into tests/conftest.py and
use it from test_core_settings and test_timezones; simplify CORE_PKG to
a plain import plus Path(mod.__file__).parent; move
test_from_options_horizon_validates_and_defaults into test_core_settings.

1575 passed.

custom_components/nestquest/__init__.py

@@ -467,10 +467,9 @@ async def async_setup_entry(hass: HomeAssistant, entry: ConfigEntry) -> bool:
         # horizon materialization and the daily-rollover listener both
         # consume it, so core never reads HA config itself.  A malformed
         # stored option falls back PER FIELD (via from_options_resilient)
-        # so a single bad sibling option cannot silently reset the user's
-        # horizon_days or day_rollover_time — the two fields core consumes
-        # — rather than the all-or-nothing reset a single try/except would
-        # cause (a malformed morning_summary_time used to wipe horizon_days).
+        # so a single bad sibling option cannot reset the user's
+        # horizon_days or day_rollover_time — the two fields core
+        # consumes — to their defaults.
         settings = NestQuestSettings.from_options_resilient(entry.options)
         remove_update_listener = entry.add_update_listener(_async_update_listener)
         remove_time_change_listener = _register_day_rollover_listener(