Notification-based block pinning (#13157)

* Worker

* Reorganize and unpin onnotification drop

* Pin in state-db, pass block number

* Pin blocks in blockchain db

* Switch to reference counted LRU

* Disable pinning when we keep all blocks

* Fix pinning hint for state-db

* Remove pinning from backend layer

* Improve readability

* Add justifications to test

* Fix justification behaviour

* Remove debug prints

* Convert channels to tracing_unbounded

* Add comments to the test

* Documentation and Cleanup

* Move task start to client

* Simplify cache

* Improve test, remove unwanted log

* Add tracing logs, remove expect for block number

* Cleanup

* Add conversion method for unpin handle to Finalitynotification

* Revert unwanted changes

* Improve naming

* Make clippy happy

* Fix docs

Co-authored-by: Michal Kucharczyk <1728078+michalkucharczyk@users.noreply.github.com>

* Use `NumberFor` instead of u64 in API

* Hand over weak reference to unpin worker task

* Unwanted

* &Hash -> Hash

* Remove number from interface, rename `_unpin_handle`, LOG_TARGET

* Move RwLock one layer up

* Apply code style suggestions

* Improve comments

* Replace lru crate by schnellru

* Only insert values for pinned items + better docs

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <git@kchr.de>

* Improve comments, log target and test

Co-authored-by: Michal Kucharczyk <1728078+michalkucharczyk@users.noreply.github.com>
Co-authored-by: Bastian Köcher <git@kchr.de>

substrate/client/api/src/in_mem.rs

@@ -788,6 +788,12 @@ where
 	fn requires_full_sync(&self) -> bool {
 		false
 	}
+
+	fn pin_block(&self, _: <Block as BlockT>::Hash) -> blockchain::Result<()> {
+		Ok(())
+	}
+
+	fn unpin_block(&self, _: <Block as BlockT>::Hash) {}
 }
 
 impl<Block: BlockT> backend::LocalBackend<Block> for Backend<Block> where Block::Hash: Ord {}