refactor(CommandParseError): remove the display implementation

we want to be able to give additional arguments to the display function later,
so this is needed

src/tokens.rs

@@ -67,12 +67,30 @@ pub enum ScanErrorKind {
     UnknownMetaCommand(String),
 }
 
+impl std::fmt::Display for ScanErrorKind {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        match self {
+            ScanErrorKind::UnexpectedChar(c) => write!(f, "unexpected char: {c:?}"),
+            ScanErrorKind::UnexpectedEndOfInput => write!(f, "unexpected end of input"),
+            ScanErrorKind::UnknownKeyword(x) => write!(f, "unknown keyword: {x:?}"),
+            ScanErrorKind::UnknownMetaCommand(x) => write!(f, "unknown meta-command: {x:?}"),
+        }
+    }
+}
+
 #[derive(Debug, Eq, PartialEq)]
 pub struct ScanError {
     pub location: Location,
     pub kind: ScanErrorKind,
 }
 
+impl std::fmt::Display for ScanError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let kind = &self.kind;
+        write!(f, "{kind}")
+    }
+}
+
 impl Tokenizer {
     fn new(input: String, file: String) -> Self {
         Self {