fix: remove Unnecessary casts

Author: petrleocompel

cryptography/lib/src/cryptography/cipher.dart

@@ -399,7 +399,7 @@ abstract class Cipher {
     String clearText, {
     required SecretKey secretKey,
   }) async {
-    final bytes = utf8.encode(clearText) as Uint8List;
+    final bytes = utf8.encode(clearText);
     final secretBox = await encrypt(
       bytes,
       secretKey: secretKey,

cryptography/lib/src/cryptography/cipher_wand.dart

@@ -177,7 +177,7 @@ abstract class CipherWand extends Wand {
   /// }
   /// ```
   Future<SecretBox> encryptString(String clearText) async {
-    final bytes = utf8.encode(clearText) as Uint8List;
+    final bytes = utf8.encode(clearText);
     final secretBox = await encrypt(
       bytes,
       possibleBuffer: bytes,