utils/errors: Track error source

in calls to `fatal`, so we keep track of the location where the panic
really originates. Otherwise, any call to `fatal` will show the code in
`errors` as source, which of course isn't true.
Also change the error formatting and do not call `to_log` for fatal
errors anymore, because the panic is already logged and contains much
more information.

zellij-utils/src/errors.rs

@@ -152,6 +152,7 @@ pub trait FatalError<T> {
     /// # Panics
     ///
     /// If the given result is an `Err` variant.
+    #[track_caller]
     fn fatal(self) -> T;
 }
 
@@ -162,17 +163,16 @@ fn discard_result<T>(_arg: anyhow::Result<T>) {}
 impl<T> FatalError<T> for anyhow::Result<T> {
     fn non_fatal(self) {
         if self.is_err() {
-            discard_result(self.context("A non-fatal error occured").to_log());
+            discard_result(self.context("a non-fatal error occured").to_log());
         }
     }
 
     fn fatal(self) -> T {
         if let Ok(val) = self {
             val
         } else {
-            self.context("A fatal error occured")
-                .to_log()
-                .expect("A fatal error occured, program terminates")
+            self.context("a fatal error occured")
+                .expect("Program terminates")
         }
     }
 }