PoV Reclaim Runtime Side (#3002)

# Runtime side for PoV Reclaim

## Implementation Overview
- Hostfunction to fetch the storage proof size has been added to the
PVF. It uses the size tracking recorder that was introduced in my
previous PR.
- Mechanisms to use the reclaim HostFunction have been introduced.
- 1. A SignedExtension that checks the node-reported proof size before
and after application of an extrinsic. Then it reclaims the difference.
- 2. A manual helper to make reclaiming easier when manual interaction
is required, for example in `on_idle` or other hooks.
- In order to utilize the manual reclaiming, I modified `WeightMeter` to
support the reduction of consumed weight, at least for storage proof
size.

## How to use
To enable the general functionality for a parachain:
1. Add the SignedExtension to your parachain runtime. 
2. Provide the HostFunction to the node
3. Enable proof recording during block import

## TODO
- [x] PRDoc

---------

Co-authored-by: Dmitry Markin <dmitry@markin.tech>
Co-authored-by: Davide Galassi <davxy@datawok.net>
Co-authored-by: Bastian Köcher <git@kchr.de>

substrate/frame/system/src/lib.rs

@@ -148,6 +148,7 @@ use sp_io::TestExternalities;
 pub mod limits;
 #[cfg(test)]
 pub(crate) mod mock;
+
 pub mod offchain;
 
 mod extensions;
@@ -847,7 +848,7 @@ pub mod pallet {
 	#[pallet::storage]
 	#[pallet::whitelist_storage]
 	#[pallet::getter(fn block_weight)]
-	pub(super) type BlockWeight<T: Config> = StorageValue<_, ConsumedWeight, ValueQuery>;
+	pub type BlockWeight<T: Config> = StorageValue<_, ConsumedWeight, ValueQuery>;
 
 	/// Total length (in bytes) for all extrinsics put together, for the current block.
 	#[pallet::storage]

substrate/primitives/weights/src/weight_meter.rs

@@ -149,6 +149,11 @@ impl WeightMeter {
 	pub fn can_consume(&self, w: Weight) -> bool {
 		self.consumed.checked_add(&w).map_or(false, |t| t.all_lte(self.limit))
 	}
+
+	/// Reclaim the given weight.
+	pub fn reclaim_proof_size(&mut self, s: u64) {
+		self.consumed.saturating_reduce(Weight::from_parts(0, s));
+	}
 }
 
 #[cfg(test)]
@@ -277,6 +282,21 @@ mod tests {
 		assert_eq!(meter.consumed(), Weight::from_parts(5, 10));
 	}
 
+	#[test]
+	#[cfg(debug_assertions)]
+	fn reclaim_works() {
+		let mut meter = WeightMeter::with_limit(Weight::from_parts(5, 10));
+
+		meter.consume(Weight::from_parts(5, 10));
+		assert_eq!(meter.consumed(), Weight::from_parts(5, 10));
+
+		meter.reclaim_proof_size(3);
+		assert_eq!(meter.consumed(), Weight::from_parts(5, 7));
+
+		meter.reclaim_proof_size(10);
+		assert_eq!(meter.consumed(), Weight::from_parts(5, 0));
+	}
+
 	#[test]
 	#[cfg(debug_assertions)]
 	#[should_panic(expected = "Weight counter overflow")]

substrate/test-utils/client/src/lib.rs

@@ -72,6 +72,7 @@ pub struct TestClientBuilder<Block: BlockT, ExecutorDispatch, Backend: 'static,
 	fork_blocks: ForkBlocks<Block>,
 	bad_blocks: BadBlocks<Block>,
 	enable_offchain_indexing_api: bool,
+	enable_import_proof_recording: bool,
 	no_genesis: bool,
 }
 
@@ -120,6 +121,7 @@ impl<Block: BlockT, ExecutorDispatch, Backend, G: GenesisInit>
 			bad_blocks: None,
 			enable_offchain_indexing_api: false,
 			no_genesis: false,
+			enable_import_proof_recording: false,
 		}
 	}
 
@@ -165,6 +167,12 @@ impl<Block: BlockT, ExecutorDispatch, Backend, G: GenesisInit>
 		self
 	}
 
+	/// Enable proof recording on import.
+	pub fn enable_import_proof_recording(mut self) -> Self {
+		self.enable_import_proof_recording = true;
+		self
+	}
+
 	/// Disable writing genesis.
 	pub fn set_no_genesis(mut self) -> Self {
 		self.no_genesis = true;
@@ -202,6 +210,7 @@ impl<Block: BlockT, ExecutorDispatch, Backend, G: GenesisInit>
 		};
 
 		let client_config = ClientConfig {
+			enable_import_proof_recording: self.enable_import_proof_recording,
 			offchain_indexing_api: self.enable_offchain_indexing_api,
 			no_genesis: self.no_genesis,
 			..Default::default()