PoV Reclaim (Clawback) Node Side (#1462)

This PR provides the infrastructure for the pov-reclaim mechanism
discussed in #209. The goal is to provide the current proof size to the
runtime so it can be used to reclaim storage weight.

## New Host Function
- A new host function is provided
[here](https://github.com/skunert/polkadot-sdk/blob/5b317fda3be205f4136f10d4490387ccd4f9765d/cumulus/primitives/pov-reclaim/src/lib.rs#L23).
It returns the size of the current proof size to the runtime. If
recording is not enabled, it returns 0.

## Implementation Overview
- Implement option to enable proof recording during import in the
client. This is currently enabled for `polkadot-parachain`,
`parachain-template` and the cumulus test node.
- Make the proof recorder ready for no-std. It was previously only
enabled for std environments, but we need to record the proof size in
`validate_block` too.
- Provide a recorder implementation that only the records the size of
incoming nodes and does not store the nodes itself.
- Fix benchmarks that were broken by async backing changes
- Provide new externalities extension that is registered by default if
proof recording is enabled.
- I think we should discuss the naming, pov-reclaim was more intuitive
to me, but we could also go with clawback like in the issue.

## Impact of proof recording during import
With proof recording: 6.3058 Kelem/s
Without proof recording: 6.3427 Kelem/s

The measured impact on the importing performance is quite low on my
machine using the block import benchmark. With proof recording I am
seeing a performance hit of 0.585%.

---------

Co-authored-by: command-bot <>
Co-authored-by: Davide Galassi <davxy@datawok.net>
Co-authored-by: Bastian Köcher <git@kchr.de>

cumulus/test/service/src/bench_utils.rs

@@ -81,8 +81,13 @@ pub fn extrinsic_set_time(client: &TestClient) -> OpaqueExtrinsic {
 pub fn extrinsic_set_validation_data(
 	parent_header: cumulus_test_runtime::Header,
 ) -> OpaqueExtrinsic {
-	let sproof_builder = RelayStateSproofBuilder { para_id: 100.into(), ..Default::default() };
 	let parent_head = HeadData(parent_header.encode());
+	let sproof_builder = RelayStateSproofBuilder {
+		para_id: cumulus_test_runtime::PARACHAIN_ID.into(),
+		included_para_head: parent_head.clone().into(),
+		..Default::default()
+	};
+
 	let (relay_parent_storage_root, relay_chain_state) = sproof_builder.into_state_root_and_proof();
 	let data = ParachainInherentData {
 		validation_data: PersistedValidationData {