implemented SD card abstraction & used it in IDStore

src/store/persistence.rs

@@ -0,0 +1,12 @@
+use alloc::vec::Vec;
+
+use crate::store::{Date, IDMapping, id_store::AttendanceDay};
+
+pub trait Persistence {
+    async fn load_day(&mut self, day: Date) -> Option<AttendanceDay>;
+    async fn save_day(&mut self, day: Date, data: &AttendanceDay);
+    async fn list_days(&mut self) -> Vec<Date>;
+
+    async fn load_mapping(&mut self) -> Option<IDMapping>;
+    async fn save_mapping(&mut self, data: &IDMapping);
+}