Enhance NVS module with a dedicated background task

- Implemented a dedicated background task to decouple long-running code from the main application task.
- Improved the NVS commit code logic, especially for batch writes to minimize flash wear.
- Updated NVS functions to support asynchronous writes and synchronous reads.
- Added default value parameters to `get` functions for better usability.
- Improved error handling and logging in NVS operations.
- Refactored related code in multiple source files to accommodate these changes.

Refs #1085, #1096 and closes #1098

README.md

@@ -31,6 +31,16 @@ Another optional feature is NVS storage, which saves the configuration permanent
 - Tilt sensitivity
 - Last tilt position
 
+### NVS Operation Details 
+When NVS storage is enabled (CONFIG_RELAY_CHN_ENABLE_NVS=y), the component creates a dedicated background task to manage all NVS write operations. This design has important implications for how you use the NVS-related functions:
+- **Asynchronous Writes:** All `set` operations (e.g., `relay_chn_flip_direction()`, `relay_chn_set_run_limit()`) are asynchronous. They add the write request to a queue and return immediately, preventing the calling task from being blocked.
+- **Synchronous Reads:** All get operations (e.g., `relay_chn_get_direction()`) are synchronous. They read the value directly from the NVS storage and will block the calling task until the read is complete.
+- **Batched Commits:** To optimize performance and minimize flash wear, the NVS task uses a batching mechanism for writes. It collects multiple write requests and commits them to the NVS flash in a single operation after a short period of inactivity (typically 200ms).
+
+> [!IMPORTANT]
+> Due to the asynchronous and batched nature of write operations, a call to a get function may not immediately reflect a value that was just written by a set function. Your application should account for this small delay.
+
+
 ## Configuration
 
 Configure the component through menuconfig under "Relay Channel Driver Configuration":