refactor: split async/sync work in stages (#4636)

Co-authored-by: Roman Krasiuk <rokrassyuk@gmail.com>

crates/interfaces/src/provider.rs

@@ -20,6 +20,9 @@ pub enum ProviderError {
     /// Error when recovering the sender for a transaction
     #[error("failed to recover sender for transaction")]
     SenderRecoveryError,
+    /// Inconsistent header gap.
+    #[error("inconsistent header gap in the database")]
+    InconsistentHeaderGap,
     /// The header number was not found for the given block hash.
     #[error("block hash {0} does not exist in Headers table")]
     BlockHashNotFound(BlockHash),