replace our DisplayWithSources with wee-woo

It's the same thing except with a nice extension trait.

src/error.rs

@@ -1,39 +1,11 @@
 //! Error handling facilities
 
-use std::{fmt, iter, path::PathBuf};
+use std::path::PathBuf;
 
 use thiserror::Error;
 
 use crate::config::ListenConfig;
 
-/// Formats an [`Error`][0] and its [`source`][1]s with a separator
-///
-/// [0]: std::error::Error
-/// [1]: std::error::Error::source
-pub(crate) struct DisplayWithSources<'a> {
-    /// The error (and its sources) to write
-    pub(crate) error: &'a dyn std::error::Error,
-
-    /// Separator to write between the original error and subsequent sources
-    pub(crate) infix: &'static str,
-}
-
-impl fmt::Display for DisplayWithSources<'_> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "{}", self.error)?;
-
-        let mut source = self.error.source();
-
-        source
-            .into_iter()
-            .chain(iter::from_fn(|| {
-                source = source.and_then(std::error::Error::source);
-                source
-            }))
-            .try_for_each(|source| write!(f, "{}{source}", self.infix))
-    }
-}
-
 /// Top-level errors
 // Missing docs are allowed here since that kind of information should be
 // encoded in the error messages themselves anyway.