feat: scan book to add to sell

lib/data/repositories/bal_repository.dart

@@ -55,6 +55,13 @@ class BalRepository {
         false;
   }
 
+  Future<Bal?> ongoingBal() async {
+    if (_bals == null) {
+      await _getBalsNoCache();
+    }
+    return _bals!.where((bal) => bal.state == BalState.ongoing).firstOrNull;
+  }
+
   Future<Result<Bal>> stopBal(int id) async {
     final result = await _apiClient.stopBal(id);
     _getBalsNoCache();

lib/data/repositories/book_instance_repository.dart

@@ -11,6 +11,10 @@ class BookInstanceRepository {
 
   final ApiClient _apiClient;
 
+  Future<Result<List<BookInstance>>> getByEan(int balId, int ean) async {
+    return await _apiClient.getBookInstanceByEAN(balId, ean);
+  }
+
   Future<Result<BookInstance>> sendBook(
     Book book,
     Owner owner,

lib/data/repositories/book_repository.dart

@@ -8,6 +8,10 @@ class BookRepository {
   final ApiClient _apiClient;
 
   Future<Result<Book>> getBookByEAN(String ean) async {
-    return _apiClient.getBookByEAN(ean);
+    return await _apiClient.getBookByEAN(ean);
+  }
+
+  Future<Result<Book>> getBookById(int id) async {
+    return await _apiClient.getBookById(id);
   }
 }

lib/data/repositories/owner_repository.dart

@@ -33,6 +33,18 @@ class OwnerRepository {
     return result;
   }
 
+  Future<Result<Owner>> getOwnerById(int id) async {
+    if (_cachedOwners != null) {
+      final result1 = _cachedOwners!
+          .where((owner) => owner.id == id)
+          .firstOrNull;
+      if (result1 != null) {
+        return Result.ok(result1);
+      }
+    }
+    return await _apiClient.getOwnerById(id);
+  }
+
   /// Adds an [Owner] to the database, and gets the resulting [Owner].
   Future<Result<Owner>> addOwner(
     String firstName,