Use CPU clock timeout for PVF jobs (#6282)

* Put in skeleton logic for CPU-time-preparation

Still needed:
- Flesh out logic
- Refactor some spots
- Tests

* Continue filling in logic for prepare worker CPU time changes

* Fix compiler errors

* Update lenience factor

* Fix some clippy lints for PVF module

* Fix compilation errors

* Address some review comments

* Add logging

* Add another log

* Address some review comments; change Mutex to AtomicBool

* Refactor handling response bytes

* Add CPU clock timeout logic for execute jobs

* Properly handle AtomicBool flag

* Use `Ordering::Relaxed`

* Refactor thread coordination logic

* Fix bug

* Add some timing information to execute tests

* Add section about the mitigation to the IG

* minor: Change more `Ordering`s to `Relaxed`

* candidate-validation: Fix build errors

polkadot/rpc/src/lib.rs

@@ -108,11 +108,7 @@ where
 		+ Sync
 		+ 'static,
 	C::Api: frame_rpc_system::AccountNonceApi<Block, AccountId, Nonce>,
-	C::Api: mmr_rpc::MmrRuntimeApi<
-		Block,
-		<Block as sp_runtime::traits::Block>::Hash,
-		BlockNumber,
-	>,
+	C::Api: mmr_rpc::MmrRuntimeApi<Block, <Block as sp_runtime::traits::Block>::Hash, BlockNumber>,
 	C::Api: pallet_transaction_payment_rpc::TransactionPaymentRuntimeApi<Block, Balance>,
 	C::Api: BabeApi<Block>,
 	C::Api: BlockBuilder<Block>,