[core] Optimize main loop with -O2

Add __attribute__((optimize("O2"))) to the main loop functions
(loop_task on ESP32, codegen loop() on other platforms) so GCC
inlines scheduler helpers and loop bookkeeping more aggressively.

Under -Os, GCC outlines small functions (Scheduler::call helpers,
millis conversions, etc.) that are called every loop iteration.
With -O2, these get inlined into the loop body, reducing call
overhead on the hottest code path in the firmware.

ESP32: loop_task grows from 303 to 416 bytes (+113 bytes).
ESP8266: no change (already fully inlined via ESPHOME_ALWAYS_INLINE).

esphome/components/esp32/core.cpp

@@ -65,7 +65,7 @@ static StaticTask_t loop_task_tcb;        // NOLINT(cppcoreguidelines-avoid-non-
 static StackType_t
     loop_task_stack[ESPHOME_LOOP_TASK_STACK_SIZE];  // NOLINT(cppcoreguidelines-avoid-non-const-global-variables)
 
-void loop_task(void *pv_params) {
+void __attribute__((optimize("O2"))) loop_task(void *pv_params) {
   setup();
   while (true) {
     App.loop();

esphome/writer.py

@@ -45,7 +45,7 @@ void setup() {
   App.setup();
 }
 
-void loop() {
+void __attribute__((optimize("O2"))) loop() {
   App.loop();
 }
 """,