PVF: Move PVF workers into separate crate (#7101)

* Move PVF workers into separate crate

* Fix indentation

* Fix compilation errors

* Fix more compilation errors

* Rename `worker.rs` files, make host interface to worker more clear

* Fix more compilation errors

* Fix more compilation errors

* Add link to issue

* Address review comments

* Update comment

polkadot/node/core/pvf/src/pvf.rs

@@ -36,13 +36,13 @@ use crate::host::tests::TEST_PREPARATION_TIMEOUT;
 #[derive(Clone, Encode, Decode)]
 pub struct PvfPrepData {
 	/// Wasm code (uncompressed)
-	pub(crate) code: Arc<Vec<u8>>,
+	code: Arc<Vec<u8>>,
 	/// Wasm code hash
-	pub(crate) code_hash: ValidationCodeHash,
+	code_hash: ValidationCodeHash,
 	/// Executor environment parameters for the session for which artifact is prepared
-	pub(crate) executor_params: Arc<ExecutorParams>,
+	executor_params: Arc<ExecutorParams>,
 	/// Preparation timeout
-	pub(crate) prep_timeout: Duration,
+	prep_timeout: Duration,
 }
 
 impl PvfPrepData {
@@ -69,15 +69,20 @@ impl PvfPrepData {
 	}
 
 	/// Returns PVF code
-	pub(crate) fn code(&self) -> Arc<Vec<u8>> {
+	pub fn code(&self) -> Arc<Vec<u8>> {
 		self.code.clone()
 	}
 
 	/// Returns executor params
-	pub(crate) fn executor_params(&self) -> Arc<ExecutorParams> {
+	pub fn executor_params(&self) -> Arc<ExecutorParams> {
 		self.executor_params.clone()
 	}
 
+	/// Returns preparation timeout.
+	pub fn prep_timeout(&self) -> Duration {
+		self.prep_timeout
+	}
+
 	/// Creates a structure for tests
 	#[cfg(test)]
 	pub(crate) fn from_discriminator_and_timeout(num: u32, timeout: Duration) -> Self {