Remove duplicated code and make base64 error handling better

src/set4.rs

@@ -1,3 +1,9 @@
+use crate::{bytes::Bytes, utils};
+
 pub fn challenge25() {
-    println!("[xxxx] Challenge 25: TBD");
+    let cipher = utils::read_base64("data/25.txt");
+    let key = Bytes::from_utf8("YELLOW SUBMARINE");
+    let _cleartext = crate::ecb::decrypt(&key, &cipher);
+
+    println!("[xxxx] Challenge 25: wip");
 }