Optimize MedianFilter memory allocation by adding vector reserve (#9531)

esphome/components/sensor/filter.cpp

@@ -50,6 +50,7 @@ optional<float> MedianFilter::new_value(float value) {
     if (!this->queue_.empty()) {
       // Copy queue without NaN values
       std::vector<float> median_queue;
+      median_queue.reserve(this->queue_.size());
       for (auto v : this->queue_) {
         if (!std::isnan(v)) {
           median_queue.push_back(v);