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>

substrate/client/block-builder/src/lib.rs

@@ -42,6 +42,7 @@ use sp_runtime::{
 use std::marker::PhantomData;
 
 pub use sp_block_builder::BlockBuilder as BlockBuilderApi;
+use sp_trie::proof_size_extension::ProofSizeExt;
 
 /// A builder for creating an instance of [`BlockBuilder`].
 pub struct BlockBuilderBuilder<'a, B, C> {
@@ -235,6 +236,10 @@ where
 
 		if record_proof {
 			api.record_proof();
+			let recorder = api
+				.proof_recorder()
+				.expect("Proof recording is enabled in the line above; qed.");
+			api.register_extension(ProofSizeExt::new(recorder));
 		}
 
 		api.set_call_context(CallContext::Onchain);