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

Kconfig

@@ -17,6 +17,12 @@ menu "Relay Channel Driver Configuration"
         help
             Number of relay channels between 1 and 8.
     
+    config RELAY_CHN_ENABLE_RUN_LIMIT
+        bool "Enable run limit for channels"
+        default n
+        help
+            Enable run limit for channels as an extra layer of output protection.
+
     config RELAY_CHN_ENABLE_TILTING
         bool "Enable tilting on relay channels"
         default n
@@ -61,4 +67,30 @@ menu "Relay Channel NVS Storage Configuration"
             The name of the custom NVS partition used for storing relay channel
             configuration. Make sure the name is exactly the same as label defined
             in the relevant partition table.
+endmenu
+
+menu "Relay Channel Run Limit Configuration"
+    depends on RELAY_CHN_ENABLE_RUN_LIMIT
+
+    config RELAY_CHN_RUN_LIMIT_MIN_SEC
+        int "Minimum run limit in seconds"
+        range 1 60
+        default 10
+        help
+            Minimum run limit in seconds for channels.
+
+    config RELAY_CHN_RUN_LIMIT_MAX_SEC
+        int "Maximum run limit in seconds"
+        range 60 3600
+        default 600
+        help
+            Maximum run limit in seconds for channels.
+
+    config RELAY_CHN_RUN_LIMIT_DEFAULT_SEC
+        int "Default run limit in seconds"
+        range 10 3600
+        default 60
+        help
+            Default run limit in seconds for channels.
+    
 endmenu