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/fat_error.rs

@@ -230,16 +230,8 @@ impl<E: fmt::Debug> From<ExpanderError<I2cDeviceError<E>>> for FatError {
     }
 }
 
-impl From<bincode::error::DecodeError> for FatError {
-    fn from(value: bincode::error::DecodeError) -> Self {
-        FatError::Eeprom24x {
-            error: format!("{value:?}"),
-        }
-    }
-}
-
-impl From<bincode::error::EncodeError> for FatError {
-    fn from(value: bincode::error::EncodeError) -> Self {
+impl From<postcard::Error> for FatError {
+    fn from(value: postcard::Error) -> Self {
         FatError::Eeprom24x {
             error: format!("{value:?}"),
         }