Refactor sr-api to not depend on client anymore (#4086)

* Refactor sr-api to not depend on client anymore

* Fix benches

* Apply suggestions from code review

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Apply suggestions from code review

substrate/core/consensus/common/src/error.rs

@@ -36,7 +36,7 @@ pub enum Error {
 	FaultyTimer(std::io::Error),
 	/// Error while working with inherent data.
 	#[display(fmt="InherentData error: {}", _0)]
-	InherentData(String),
+	InherentData(inherents::Error),
 	/// Unable to propose a block.
 	#[display(fmt="Unable to create block proposal.")]
 	CannotPropose,