Add extra logging for external formatters and formatting errors

This should help debug formatting failures when using external
formatters in the future. Previously we didn't log anything when an
external formatter failed despite having a custom error type for it.

helix-term/src/commands.rs

@@ -3438,7 +3438,8 @@ async fn make_format_callback(
         let doc = doc_mut!(editor, &doc_id);
         let view = view_mut!(editor, view_id);
 
-        if let Ok(format) = format {
+        match format {
+            Ok(format) => {
                 if doc.version() == doc_version {
                     doc.apply(&format, view.id);
                     doc.append_changes_to_history(view);
@@ -3448,6 +3449,10 @@ async fn make_format_callback(
                     log::info!("discarded formatting changes because the document changed");
                 }
             }
+            Err(err) => {
+                log::info!("failed to format '{}': {err}", doc.display_name());
+            }
+        }
 
         if let Some((path, force)) = write {
             let id = doc.id();

helix-view/src/document.rs

@@ -772,6 +772,11 @@ pub fn format(&self) -> Option<BoxFuture<'static, Result<Transaction, FormatterE
                 ))
             })
         {
+            log::debug!(
+                "formatting '{}' with command '{}', args {fmt_args:?}",
+                self.display_name(),
+                fmt_cmd.display(),
+            );
             use std::process::Stdio;
             let text = self.text().clone();