Add a proper error type to ContinuallyRan

This isn't necessary. Because we just log the error, we never match off of it,
we don't need any structure beyond String (or now Debug, which still gives us
a way to print the error). This is for the ergonomics of not having to
constantly write `.map_err(|e| format!("{e:?}"))`.

common/task/src/lib.rs

@@ -2,7 +2,11 @@
 #![doc = include_str!("../README.md")]
 #![deny(missing_docs)]
 
-use core::{future::Future, time::Duration};
+use core::{
+  fmt::{self, Debug},
+  future::Future,
+  time::Duration,
+};
 
 use tokio::sync::mpsc;
 
@@ -60,6 +64,15 @@ impl TaskHandle {
   }
 }
 
+/// An enum which can't be constructed, representing that the task does not error.
+pub enum DoesNotError {}
+impl Debug for DoesNotError {
+  fn fmt(&self, _: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
+    // This type can't be constructed so we'll never have a `&self` to call this fn with
+    unreachable!()
+  }
+}
+
 /// A task to be continually ran.
 pub trait ContinuallyRan: Sized + Send {
   /// The amount of seconds before this task should be polled again.
@@ -69,11 +82,14 @@ pub trait ContinuallyRan: Sized + Send {
   /// Upon error, the amount of time waited will be linearly increased until this limit.
   const MAX_DELAY_BETWEEN_ITERATIONS: u64 = 120;
 
+  /// The error potentially yielded upon running an iteration of this task.
+  type Error: Debug;
+
   /// Run an iteration of the task.
   ///
   /// If this returns `true`, all dependents of the task will immediately have a new iteration ran
   /// (without waiting for whatever timer they were already on).
-  fn run_iteration(&mut self) -> impl Send + Future<Output = Result<bool, String>>;
+  fn run_iteration(&mut self) -> impl Send + Future<Output = Result<bool, Self::Error>>;
 
   /// Continually run the task.
   fn continually_run(
@@ -115,12 +131,17 @@ pub trait ContinuallyRan: Sized + Send {
             }
           }
           Err(e) => {
-            log::warn!("{}", e);
+            log::warn!("{e:?}");
             increase_sleep_before_next_task(&mut current_sleep_before_next_task);
           }
         }
 
         // Don't run the task again for another few seconds UNLESS told to run now
+        /*
+          We could replace tokio::mpsc with async_channel, tokio::time::sleep with
+          patchable_async_sleep::sleep, and tokio::select with futures_lite::future::or
+          It isn't worth the effort when patchable_async_sleep::sleep will still resolve to tokio
+        */
         tokio::select! {
           () = tokio::time::sleep(Duration::from_secs(current_sleep_before_next_task)) => {},
           msg = task.run_now.recv() => {