Partial fee estimates for SubmittableExtrinsic (#910)

* add partial_fee estimation to submittable extrinsic

* add integration test

* make functions immune to doctest

* add doc test

* inline encoded_with_len, fix tests

* fix test fmt

* remove unused imoort

* Bump h2 from 0.3.16 to 0.3.17 (#911)

Bumps [h2](https://github.com/hyperium/h2) from 0.3.16 to 0.3.17.
- [Release notes](https://github.com/hyperium/h2/releases)
- [Changelog](https://github.com/hyperium/h2/blob/master/CHANGELOG.md)
- [Commits](https://github.com/hyperium/h2/compare/v0.3.16...v0.3.17)

---
updated-dependencies:
- dependency-name: h2
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

* call_raw returns Res: Decode

* remove import

* remove struct

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

subxt/src/client/online_client.rs

@@ -17,7 +17,7 @@ use crate::{
     tx::TxClient,
     Config, Metadata,
 };
-use codec::{Compact, Decode};
+use codec::Compact;
 use derivative::Derivative;
 use frame_metadata::RuntimeMetadataPrefixed;
 use futures::future;
@@ -136,10 +136,9 @@ impl<T: Config> OnlineClient<T> {
 
     /// Fetch the metadata from substrate using the runtime API.
     async fn fetch_metadata(rpc: &Rpc<T>) -> Result<Metadata, Error> {
-        let bytes = rpc.state_call("Metadata_metadata", None, None).await?;
-        let cursor = &mut &*bytes;
-        let _ = <Compact<u32>>::decode(cursor)?;
-        let meta: RuntimeMetadataPrefixed = Decode::decode(cursor)?;
+        let (_, meta) = rpc
+            .state_call::<(Compact<u32>, RuntimeMetadataPrefixed)>("Metadata_metadata", None, None)
+            .await?;
         Ok(meta.try_into()?)
     }