Refactor to remove redundant initialization and add NVS storage tests

- Removed unnecessary calls to relay_chn_create and g_is_component_initialized in multiple test cases across test_relay_chn_core_single.c, test_relay_chn_listener_multi.c, and test_relay_chn_listener_single.c.
- Introduced new test files for NVS functionality: test_relay_chn_nvs_multi.c and test_relay_chn_nvs_single.c, covering initialization, direction setting, invalid parameters, and erase operations.
- Updated partition table configuration to support NVS storage, including the addition of a new partition file part_nvs.csv.
- Adjusted sdkconfig files to enable NVS support and configure custom partition settings for relay channels.

test_apps/sdkconfig.defaults.custom_nvs

@@ -0,0 +1,15 @@
+# Disable task WDT for tests
+CONFIG_ESP_TASK_WDT_INIT=n
+
+# Partition configuration
+CONFIG_PARTITION_TABLE_SINGLE_APP=y
+CONFIG_PARTITION_TABLE_CUSTOM=y
+CONFIG_PARTITION_TABLE_CUSTOM_FILENAME="partitions/part_nvs.csv"
+
+# Relay Channel Driver Default Configuration for Testing
+# Keep this as short as possible for tests
+CONFIG_RELAY_CHN_OPPOSITE_INERTIA_MS=200
+CONFIG_RELAY_CHN_COUNT=2
+CONFIG_RELAY_CHN_ENABLE_TILTING=y
+CONFIG_RELAY_CHN_ENABLE_NVS=y
+CONFIG_RELAY_CHN_NVS_CUSTOM_PARTITION=y