Implement BlocksClient for working with blocks (#671)

* rpc: Fill in any missing finalized blocks

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* tests: Move fill blocks test to RPC location

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* events: Remove the fill in strategy

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* blocks: Introduce blocks client

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* client: Enable the block API

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* blocks: Simplify `subscribe_finalized_headers` method

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* tests: Add tests for `subscribe_finalized_headers`

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* blocks: Implement `subscribe_headers`

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* tests: Add tests for `subscribe_headers`

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* tests: Move `missing_block_headers_will_be_filled_in` to blocks

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* events: Use the new subscribe to blocks

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* blocks: Change API to return future similar to events

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* events: Use blocks API for subscribing to blocks

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Update subxt/src/blocks/blocks_client.rs

Co-authored-by: James Wilson <james@jsdw.me>

* blocks: Simplify docs for `subscribe_finalized_headers`

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* blocks: Use `PhantomDataSendSync` to avoid other bounds on `T: Config`

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* blocks: Add docs for best blocks

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* blocks: Avoid one clone for the `client.rpc()`

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

* Update testing/integration-tests/src/blocks/mod.rs

Co-authored-by: Niklas Adolfsson <niklasadolfsson1@gmail.com>

* blocks: Improve `subscribe_headers` doc

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>
Co-authored-by: James Wilson <james@jsdw.me>
Co-authored-by: Niklas Adolfsson <niklasadolfsson1@gmail.com>

subxt/src/client/offline_client.rs

@@ -3,6 +3,7 @@
 // see LICENSE for license details.
 
 use crate::{
+    blocks::BlocksClient,
     constants::ConstantsClient,
     events::EventsClient,
     rpc::RuntimeVersion,
@@ -43,6 +44,11 @@ pub trait OfflineClientT<T: Config>: Clone + Send + Sync + 'static {
     fn constants(&self) -> ConstantsClient<T, Self> {
         ConstantsClient::new(self.clone())
     }
+
+    /// Work with blocks.
+    fn blocks(&self) -> BlocksClient<T, Self> {
+        BlocksClient::new(self.clone())
+    }
 }
 
 /// A client that is capable of performing offline-only operations.