Improve Dispatch Errors (#878)

* better dispatch errors

* dry_run to use same DispatchError

* fix dry_run_fails; use correct transfer amount

* Hide ModuleError impl and avoid pulling details from metadata unless user needs them

* fix tests

* actually fix the tests (hopefully..)

* Add a couple more DispatchError test cases

* Add a comment about where the error was copied from

* Also expose a way to obtain the raw module error data

* Remove redundant variant prefixes

* explicit lifetime on From<str> for clarity

* fmt

subxt/src/tx/tx_client.rs

@@ -462,6 +462,7 @@ where
     ///
     /// Returns `Ok` with a [`DryRunResult`], which is the result of attempting to dry run the extrinsic.
     pub async fn dry_run(&self, at: Option<T::Hash>) -> Result<DryRunResult, Error> {
-        self.client.rpc().dry_run(self.encoded(), at).await
+        let dry_run_bytes = self.client.rpc().dry_run(self.encoded(), at).await?;
+        dry_run_bytes.into_dry_run_result(&self.client.metadata())
     }
 }