Prep to release v0.42.0 (#2003)

* Prep to release v0.42.0

* Remove test_context reference from example

* standalone_crate for doc tests because codegen is expensive

* fmt

subxt/src/backend/mod.rs

@@ -29,7 +29,7 @@ pub mod rpc {
         ///
         /// # Example
         ///
-        /// ```rust,no_run
+        /// ```rust,no_run,standalone_crate
         /// use std::time::Duration;
         /// use futures::StreamExt;
         /// use subxt::backend::rpc::reconnecting_rpc_client::{RpcClient, ExponentialBackoff};
@@ -541,7 +541,7 @@ mod test {
         /// - `current_runtime_version`
         /// - `call`
         /// The test covers them because they follow the simple pattern of:
-        /// ```no_run
+        /// ```rust,no_run,standalone_crate
         ///  async fn THE_THING(&self) -> Result<HashFor<T>, Error> {
         ///    retry(|| <DO THE THING> ).await
         ///  }
@@ -572,7 +572,7 @@ mod test {
         /// - `stream_all_block_headers`
         /// - `stream_best_block_headers`
         /// The test covers them because they follow the simple pattern of:
-        /// ```no_run
+        /// ```rust,no_run,standalone_crate
         /// async fn stream_the_thing(
         ///     &self,
         /// ) -> Result<StreamOfResults<(T::Header, BlockRef<HashFor<T>>)>, Error> {

subxt/src/backend/utils.rs

@@ -89,7 +89,7 @@ impl<T> Stream for RetrySubscription<T> {
 ///
 /// # Example
 ///
-/// ```no_run
+/// ```rust,no_run,standalone_crate
 /// use subxt::backend::utils::retry;
 ///
 /// async fn some_future() -> Result<(), subxt::error::Error> {
@@ -149,7 +149,7 @@ where
 ///
 /// # Example
 ///
-/// ```no_run
+/// ```rust,no_run,standalone_crate
 /// use subxt::backend::{utils::retry_stream, StreamOf};
 /// use futures::future::FutureExt;
 ///