[esp8266_pwm] Skip the frequency setter when it matches the default (#19224)

tests/component_tests/esp8266_pwm/config/frequency.yaml

@@ -0,0 +1,19 @@
+---
+esphome:
+  name: test
+
+esp8266:
+  board: d1_mini
+
+output:
+  - platform: esp8266_pwm
+    id: default_frequency
+    pin: GPIO4
+    frequency: 1kHz
+  - platform: esp8266_pwm
+    id: custom_frequency
+    pin: GPIO5
+    frequency: 2kHz
+  - platform: esp8266_pwm
+    id: schema_default_frequency
+    pin: GPIO12

tests/component_tests/esp8266_pwm/test_esp8266_pwm.py

@@ -0,0 +1,16 @@
+"""Tests for the esp8266_pwm output codegen."""
+
+from collections.abc import Callable
+from pathlib import Path
+
+
+def test_default_frequency_is_not_emitted(
+    generate_main: Callable[[str | Path], str],
+    component_config_path: Callable[[str], Path],
+) -> None:
+    """The 1 kHz default already lives in the C++ initializer."""
+    main_cpp = generate_main(component_config_path("frequency.yaml"))
+
+    assert "default_frequency->set_frequency(" not in main_cpp
+    assert "schema_default_frequency->set_frequency(" not in main_cpp
+    assert "custom_frequency->set_frequency(2000.0f);" in main_cpp