Migrate serialization from Bincode to Postcard

- Replaced Bincode with Postcard for serialization/deserialization across configs and save operations.
- Simplified struct derives by removing `bincode`-specific traits.
- Updated `Cargo.toml` and `Cargo.lock` to include `postcard` and dependencies.
- Added padding stripping for deserialization and improved error handling.
- Adjusted serialization logic in `savegame_manager.rs` and related modules.

Software/MainBoard/rust/src/hal/savegame_manager.rs

@@ -1,3 +1,4 @@
+use alloc::string::ToString;
 use alloc::vec::Vec;
 use embedded_savegame::storage::{Flash, Storage};
 use embedded_storage::nor_flash::{NorFlash, ReadNorFlash};
@@ -32,6 +33,19 @@ struct ParsedSave<'a> {
     data: &'a [u8],
 }
 
+fn strip_padding(data: &[u8]) -> &[u8] {
+    let mut end = data.len();
+    while end > 0 {
+        let b = data[end - 1];
+        if b == 0x00 || b == 0xFF {
+            end -= 1;
+        } else {
+            break;
+        }
+    }
+    &data[..end]
+}
+
 fn parse_save(data: &[u8]) -> FatResult<ParsedSave<'_>> {
     if data.len() < SAVE_HEADER_LEN {
         return Err(FatError::String {
@@ -60,7 +74,7 @@ fn parse_save(data: &[u8]) -> FatResult<ParsedSave<'_>> {
 
     Ok(ParsedSave {
         created_at,
-        data: &data[timestamp_end..],
+        data: strip_padding(&data[timestamp_end..]),
     })
 }
 
@@ -240,7 +254,7 @@ impl SavegameManager {
                         saves.push(SaveInfo {
                             idx,
                             len: 0,
-                            created_at: None,
+                            created_at: Some(err.to_string()),
                         });
                     }
                 }