[sensor] Drop incorrect O(1) complexity claim from timeout filter comment

set_timer_common_'s self-key cancel path scans items_ and to_add_ linearly,
so the cancel-and-replace is O(N) in the global scheduler item count, not
O(1). Reword to describe the behavior without the complexity claim.

Address Copilot review feedback.

esphome/components/sensor/filter.cpp

@@ -323,8 +323,8 @@ optional<float> or_filter_new_value(Filter **filters, size_t count, float value,
 }
 
 // TimeoutFilterLast - "last" mode: re-arm on every input; output the latest value if no further
-// input arrives within time_period_. Self-keyed scheduler.set_timeout(this, ...) cancels and
-// replaces any pending arm in O(1).
+// input arrives within time_period_. Self-keyed scheduler.set_timeout(this, ...) cancels any
+// pending arm with the same self-key and installs a new one.
 optional<float> TimeoutFilterLast::new_value(float value) {
   this->pending_value_ = value;
   App.scheduler.set_timeout(this, this->time_period_, [this]() { this->output(this->pending_value_); });