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_core.h

@@ -33,6 +33,20 @@ ESP_EVENT_DECLARE_BASE(RELAY_CHN_CMD_EVENT);
  */
 esp_err_t relay_chn_init_timer(relay_chn_ctl_t *chn_ctl);
 
+#if RELAY_CHN_ENABLE_RUN_LIMIT == 1
+/**
+ * @brief Initializes the relay channel run limit timer.
+ * 
+ * This function creates a timer for the relay channel to handle run time limit.
+ * Required by *_ctl_* module.
+ * 
+ * @param chn_ctl Pointer to the relay channel control structure.
+ * 
+ * @return esp_err_t ESP_OK on success, or an error code on failure.
+ */
+esp_err_t relay_chn_init_run_limit_timer(relay_chn_ctl_t *chn_ctl);
+#endif // RELAY_CHN_ENABLE_RUN_LIMIT
+
 /**
  * @brief Issues a command to the relay channel.
  *