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:?}"))`.

processor/scanner/src/batch/mod.rs

@@ -7,7 +7,10 @@ use serai_db::{DbTxn, Db};
 
 use serai_in_instructions_primitives::{MAX_BATCH_SIZE, Batch};
 
-use primitives::{EncodableG, task::ContinuallyRan};
+use primitives::{
+  EncodableG,
+  task::{DoesNotError, ContinuallyRan},
+};
 use crate::{
   db::{Returnable, ScannerGlobalDb, InInstructionData, ScanToBatchDb, BatchData, BatchToReportDb},
   index,
@@ -60,7 +63,9 @@ impl<D: Db, S: ScannerFeed> BatchTask<D, S> {
 }
 
 impl<D: Db, S: ScannerFeed> ContinuallyRan for BatchTask<D, S> {
-  fn run_iteration(&mut self) -> impl Send + Future<Output = Result<bool, String>> {
+  type Error = DoesNotError;
+
+  fn run_iteration(&mut self) -> impl Send + Future<Output = Result<bool, Self::Error>> {
     async move {
       let highest_batchable = {
         // Fetch the next to scan block

processor/scanner/src/eventuality/mod.rs

@@ -190,7 +190,9 @@ impl<D: Db, S: ScannerFeed, Sch: Scheduler<S>> EventualityTask<D, S, Sch> {
 }
 
 impl<D: Db, S: ScannerFeed, Sch: Scheduler<S>> ContinuallyRan for EventualityTask<D, S, Sch> {
-  fn run_iteration(&mut self) -> impl Send + Future<Output = Result<bool, String>> {
+  type Error = String;
+
+  fn run_iteration(&mut self) -> impl Send + Future<Output = Result<bool, Self::Error>> {
     async move {
       // Fetch the highest acknowledged block
       let Some(highest_acknowledged) = ScannerGlobalDb::<S>::highest_acknowledged_block(&self.db)

processor/scanner/src/index/mod.rs

@@ -58,7 +58,9 @@ impl<D: Db, S: ScannerFeed> IndexTask<D, S> {
 }
 
 impl<D: Db, S: ScannerFeed> ContinuallyRan for IndexTask<D, S> {
-  fn run_iteration(&mut self) -> impl Send + Future<Output = Result<bool, String>> {
+  type Error = String;
+
+  fn run_iteration(&mut self) -> impl Send + Future<Output = Result<bool, Self::Error>> {
     async move {
       // Fetch the latest finalized block
       let our_latest_finalized = IndexDb::latest_finalized_block(&self.db)

processor/scanner/src/report/mod.rs

@@ -4,7 +4,7 @@ use serai_db::{DbTxn, Db};
 
 use serai_validator_sets_primitives::Session;
 
-use primitives::task::ContinuallyRan;
+use primitives::task::{DoesNotError, ContinuallyRan};
 use crate::{
   db::{BatchData, BatchToReportDb, BatchesToSign},
   substrate, ScannerFeed,
@@ -27,7 +27,9 @@ impl<D: Db, S: ScannerFeed> ReportTask<D, S> {
 }
 
 impl<D: Db, S: ScannerFeed> ContinuallyRan for ReportTask<D, S> {
-  fn run_iteration(&mut self) -> impl Send + Future<Output = Result<bool, String>> {
+  type Error = DoesNotError;
+
+  fn run_iteration(&mut self) -> impl Send + Future<Output = Result<bool, Self::Error>> {
     async move {
       let mut made_progress = false;
       loop {

processor/scanner/src/scan/mod.rs

@@ -98,7 +98,9 @@ impl<D: Db, S: ScannerFeed> ScanTask<D, S> {
 }
 
 impl<D: Db, S: ScannerFeed> ContinuallyRan for ScanTask<D, S> {
-  fn run_iteration(&mut self) -> impl Send + Future<Output = Result<bool, String>> {
+  type Error = String;
+
+  fn run_iteration(&mut self) -> impl Send + Future<Output = Result<bool, Self::Error>> {
     async move {
       // Fetch the safe to scan block
       let latest_scannable =

processor/scanner/src/substrate/mod.rs

@@ -5,7 +5,7 @@ use serai_db::{Get, DbTxn, Db};
 use serai_coins_primitives::{OutInstruction, OutInstructionWithBalance};
 
 use messages::substrate::ExecutedBatch;
-use primitives::task::ContinuallyRan;
+use primitives::task::{DoesNotError, ContinuallyRan};
 use crate::{
   db::{ScannerGlobalDb, SubstrateToEventualityDb, AcknowledgedBatches},
   index, batch, ScannerFeed, KeyFor,
@@ -50,7 +50,9 @@ impl<D: Db, S: ScannerFeed> SubstrateTask<D, S> {
 }
 
 impl<D: Db, S: ScannerFeed> ContinuallyRan for SubstrateTask<D, S> {
-  fn run_iteration(&mut self) -> impl Send + Future<Output = Result<bool, String>> {
+  type Error = DoesNotError;
+
+  fn run_iteration(&mut self) -> impl Send + Future<Output = Result<bool, Self::Error>> {
     async move {
       let mut made_progress = false;
       loop {