chore: fix typos and link broken (#1541)

Signed-off-by: snoppy <michaleli@foxmail.com>

subxt/src/backend/mod.rs

@@ -103,7 +103,7 @@ pub trait Backend<T: Config>: sealed::Sealed + Send + Sync + 'static {
     ) -> Result<Vec<u8>, Error>;
 }
 
-/// helpeful utility methods derived from those provided on [`Backend`]
+/// helpful utility methods derived from those provided on [`Backend`]
 #[async_trait]
 pub trait BackendExt<T: Config>: Backend<T> {
     /// Fetch a single value from storage.

subxt/src/backend/unstable/follow_stream_unpin.rs

@@ -394,7 +394,7 @@ type UnpinFlags<Hash> = Arc<Mutex<HashSet<Hash>>>;
 
 #[derive(Debug)]
 struct PinnedDetails<Hash: BlockHash> {
-    /// Realtively speaking, how old is the block? When we start following
+    /// Relatively speaking, how old is the block? When we start following
     /// blocks, the first finalized block gets an age of 0, the second an age
     /// of 1 and so on.
     rel_block_age: usize,

subxt/src/backend/unstable/mod.rs

@@ -545,7 +545,7 @@ impl<T: Config + Send + Sync + 'static> Backend<T> for UnstableBackend<T> {
                         }
                         FollowEvent::Stop => {
                             // If we get this event, we'll lose all of our existing pinned blocks and have a gap
-                            // in which we may lose the finaliuzed block that the TX is in. For now, just error if
+                            // in which we may lose the finalized block that the TX is in. For now, just error if
                             // this happens, to prevent the case in which we never see a finalized block and wait
                             // forever.
                             return Poll::Ready(err_other("chainHead_follow emitted 'stop' event during transaction submission"));