assembler: purge unwrap and use more AssembleErrors

assembler/src/util/mod.rs

@@ -4,8 +4,10 @@ use std::io::Write;
 
 pub fn input(prompt: &str) -> String {
     print!("{prompt}\n > ");
-    std::io::stdout().flush().unwrap();
+    std::io::stdout().flush().expect("Failed to flush stdout");
     let mut input = String::new();
-    std::io::stdin().read_line(&mut input).unwrap();
+    std::io::stdin()
+        .read_line(&mut input)
+        .expect("Failed to read line from stdin");
     input.trim().to_string()
 }