Expand NVRAM trait with integrity validation helpers (#11)

Related to
OpenDevicePartnership/embassy-imxrt#538. This PR
adds two helper functions to the NVRAM trait which makes it easy for a
user to obtain the contents of an NVRAM table for validation and then
clear them if found to be invalid.

Author: madeleyneVaca

embedded-mcu-hal/src/nvram.rs

@@ -14,7 +14,23 @@ pub trait NvramStorage<'a, T>: Send {
 pub trait Nvram<'a, StorageType, StoredType, const CELL_COUNT: usize>: Send
 where
     StorageType: NvramStorage<'a, StoredType>,
+    StoredType: Copy,
 {
     /// Returns an array of mutable storage cells.
+    ///
+    /// This method borrows the NVRAM for its entire lifetime to prevent double-borrowing
+    /// of the underlying hardware. It can effectively only be called once per instance.
     fn storage(&'a mut self) -> &'a mut [StorageType; CELL_COUNT];
+
+    /// Dumps the contents of all storage cells into an array.
+    /// This is for integrity validation purposes and not an alternative to `storage`.
+    fn dump_storage(&self) -> [StoredType; CELL_COUNT];
+
+    /// Clears all storage cells to an implementation-defined cleared state.
+    ///
+    /// StoredType implementations should document their clearing behavior. For numeric
+    /// types like u32, this is commonly zero.
+    /// Best practice is to use this API, if needed, during device initialization to ensure
+    /// a known state prior to calling `storage()` and utilizing the NVRAM cells.
+    fn clear_storage(&mut self);
 }