[core] Factor trim_freelist() vector shrink into out-of-line helper

The three swap-with-copy lines in trim_freelist() inlined the
construct-swap-destruct dance per call site, costing ~440 B flash on ESP32.
Move the swap-shrink into a noinline private static helper so all three
callers share one body. Net flash cost of vector shrinking drops to ~296 B
(from ~444 B) while preserving the same RAM-reclaim behaviour.

shrink_to_fit() is a non-binding hint that the toolchain ignores, so the
swap-with-copy idiom is still required.

esphome/core/scheduler.cpp

@@ -899,6 +899,14 @@ void Scheduler::recycle_item_main_loop_(SchedulerItem *item) {
 #endif
 }
 
+// Shrink a SchedulerItem* vector's capacity to its current size via the swap-with-copy
+// idiom (std::vector::shrink_to_fit() is non-binding and our toolchain ignores it).
+// Out-of-line + noinline so the callers in trim_freelist() share one body instead of
+// inlining the construct-swap-destruct dance per call site (~440 B flash on ESP32).
+void __attribute__((noinline)) Scheduler::shrink_scheduler_vector_(std::vector<SchedulerItem *> *v) {
+  std::vector<SchedulerItem *>(*v).swap(*v);
+}
+
 void Scheduler::trim_freelist() {
   LockGuard guard{this->lock_};
   SchedulerItem *item = this->scheduler_item_pool_head_;
@@ -915,13 +923,12 @@ void Scheduler::trim_freelist() {
   this->scheduler_item_pool_head_ = nullptr;
   this->scheduler_item_pool_size_ = 0;
 
-  // The vectors that back items_/to_add_/defer_queue_ also retain their boot-peak
-  // capacity (std::vector grows by doubling). Swap each with a same-content copy to
-  // reclaim the slack -- the new vector is sized exactly to its current contents.
-  std::vector<SchedulerItem *>(this->items_).swap(this->items_);
-  std::vector<SchedulerItem *>(this->to_add_).swap(this->to_add_);
+  // items_/to_add_/defer_queue_ retain their boot-peak vector capacity (vector grows
+  // by doubling and otherwise keeps the peak). Reclaim that slack as well.
+  shrink_scheduler_vector_(&this->items_);
+  shrink_scheduler_vector_(&this->to_add_);
 #ifndef ESPHOME_THREAD_SINGLE
-  std::vector<SchedulerItem *>(this->defer_queue_).swap(this->defer_queue_);
+  shrink_scheduler_vector_(&this->defer_queue_);
 #endif
 
 #ifdef ESPHOME_DEBUG_SCHEDULER

esphome/core/scheduler.h

@@ -365,6 +365,10 @@ class Scheduler {
   SchedulerItem *get_item_from_pool_locked_();
 
  private:
+  // Out-of-line helper that shrinks a SchedulerItem* vector's capacity to its current
+  // size. Centralised so trim_freelist() doesn't pay flash cost per call site.
+  static void shrink_scheduler_vector_(std::vector<SchedulerItem *> *v);
+
   // Helper to cancel matching items - must be called with lock held.
   // When find_first=true, stops after the first match (used by set_timer_common_ where
   // the cancel-before-add invariant guarantees at most one match).