fatality based errors (#4448)

* seed commit for fatality based errors

* fatality

* first draft of fatality

* cleanup

* differnt approach

* simplify

* first working version for enums, with documentation

* add split

* fix simple split test case

* extend README.md

* update fatality impl

* make tests passed

* apply fatality to first subsystem

* fatality fixes

* use fatality in a subsystem

* fix subsystemg

* fixup proc macro

* fix/test: log::*! do not execute when log handler is missing

* fix spelling

* rename Runtime2 to something sane

* allow nested split with `forward` annotations

* add free license

* enable and fixup all tests

* use external fatality

Makes this more reviewable.

* bump fatality dep

Avoid duplicate expander compilations.

* migrate availability distribution

* more fatality usage

* chore: bump fatality to 0.0.6

* fixup remaining subsystems

* chore: fmt

* make cargo spellcheck happy

* remove single instance of `#[fatal(false)]`

* last quality sweep

* fixup

polkadot/node/network/availability-distribution/src/requester/mod.rs

@@ -39,8 +39,7 @@ use polkadot_subsystem::{
 	ActivatedLeaf, ActiveLeavesUpdate, LeafStatus, SubsystemContext,
 };
 
-use super::{Metrics, Result, LOG_TARGET};
-use crate::error::Fatal;
+use super::{FatalError, Metrics, Result, LOG_TARGET};
 
 #[cfg(test)]
 mod tests;
@@ -324,6 +323,9 @@ where
 	})
 	.await;
 
-	let ancestors = rx.await.map_err(Fatal::ChainApiSenderDropped)?.map_err(Fatal::ChainApi)?;
+	let ancestors = rx
+		.await
+		.map_err(FatalError::ChainApiSenderDropped)?
+		.map_err(FatalError::ChainApi)?;
 	Ok(ancestors)
 }