Add run limit feature for relay channels with NVS support

- Introduced configuration options for enabling run limits in Kconfig.
- Added APIs to get and set run limits for individual relay channels.
- Implemented run limit timer functionality to automatically stop channels.
- Updated NVS handling to store and retrieve run limit values.
- Enhanced documentation in README and code comments to reflect new feature.

Closes #1080

private_include/relay_chn_nvs.h

@@ -45,6 +45,26 @@ esp_err_t relay_chn_nvs_set_direction(uint8_t ch, relay_chn_direction_t directio
  */
 esp_err_t relay_chn_nvs_get_direction(uint8_t ch, relay_chn_direction_t *direction);
 
+#if RELAY_CHN_ENABLE_RUN_LIMIT == 1
+/**
+ * @brief Store relay channel run limit in NVS.
+ *
+ * @param[in] ch Channel number.
+ * @param[in] direction Run limit value to store.
+ * @return ESP_OK on success, error code otherwise.
+ */
+esp_err_t relay_chn_nvs_set_run_limit(uint8_t ch, uint16_t time_sec);
+
+/**
+ * @brief Retrieve relay channel run limit from NVS.
+ *
+ * @param[in] ch Channel number.
+ * @param[out] direction Pointer to store retrieved run limit value.
+ * @return ESP_OK on success, error code otherwise.
+ */
+esp_err_t relay_chn_nvs_get_run_limit(uint8_t ch, uint16_t *time_sec);
+#endif // RELAY_CHN_ENABLE_RUN_LIMIT == 1
+
 #ifdef RELAY_CHN_ENABLE_TILTING
 /**
  * @brief Store tilt sensitivity in NVS.