fix: don't let an in-progress settle window block a second write's own optimistic apply

Widening the settle window to tens of seconds (previous commit) made a
real gap much more likely to bite: apply() gated every source,
including 'optimistic', on _is_settling. /course/vs/0 backs several
independent washer selects (cycle, detergent quantity, softener
quantity, ...), so picking a second one while the first write's window
was still open -- routine within a ~43s window -- had its own
optimistic value silently dropped from the cache instead of shown,
recreating the exact "write doesn't seem to apply" symptom the guard
exists to prevent, just for whichever write lost the race.

Let source='optimistic' always bypass the gate; poll/sweep/observe
stay gated as before. mark_write_pending still re-arms the window
right after, so the newer write is protected going forward.

custom_components/localthings/observe.py

@@ -115,8 +115,22 @@ class ObserveManager:
         could each read the same prior rep and the second writer would
         silently lose the first's fields, reintroducing the exact bug
         this merge fixes.
+
+        `source == 'optimistic'` always bypasses the settle gate below,
+        even while this href is already settling from an earlier write.
+        Several independent selects can share one href -- issue #9's washer
+        packs cycle, detergent, and softener settings onto the same
+        /course/vs/0 -- so a second, different write to the same href
+        while the first's settle window is still open (up to
+        _POST_TIMEOUT_S + _POLL_TIMEOUT_S, tens of seconds -- see
+        coordinator.async_send_command) is an expected, normal sequence,
+        not a stale echo of the first write. Gating it the same as a
+        poll/sweep/observe update would silently drop the user's own
+        second selection from the cache until the first write's guard
+        happened to expire, i.e. the exact symptom this guard exists to
+        prevent, just relocated to whichever write loses the race.
         """
-        if self._is_settling(href):
+        if source != 'optimistic' and self._is_settling(href):
             self.log.debug("dropping %s update for %s (settling)", source, href)
             return False
         with self._cache_lock: