Expose more syncing types to enable custom syncing strategy (#6163)

This PR exposes additional syncing types to facilitate the development
of a custom syncing strategy based on the existing Polkadot syncing
strategy. Specifically, my goal is to isolate the state sync and chain
sync components, allowing the state to be downloaded from the P2P
network without running a full regular Substrate node. I also need to
intercept the state responses during the state sync process.

The newly exposed types are necessary to implement this custom syncing
strategy.

prdoc/pr_6163.prdoc

+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: Expose more syncing types to enable custom syncing strategy
+
+doc:
+  - audience: Node Dev
+    description: |
+      Exposes additional syncing types to facilitate the development of a custom syncing strategy.
+
+crates:
+  - name: sc-network-sync
+    bump: patch

substrate/client/network/sync/src/lib.rs

@@ -18,6 +18,7 @@
 
 //! Blockchain syncing implementation in Substrate.
 
+pub use schema::v1::*;
 pub use service::syncing_service::SyncingService;
 pub use strategy::warp::{WarpSyncConfig, WarpSyncPhase, WarpSyncProgress};
 pub use types::{SyncEvent, SyncEventStream, SyncState, SyncStatus, SyncStatusProvider};

substrate/client/network/sync/src/strategy.rs

@@ -25,7 +25,7 @@
 pub mod chain_sync;
 mod disconnected_peers;
 pub mod polkadot;
-mod state;
+pub mod state;
 pub mod state_sync;
 pub mod warp;
 
@@ -177,7 +177,8 @@ pub enum SyncingAction<B: BlockT> {
 }
 
 impl<B: BlockT> SyncingAction<B> {
-	fn is_finished(&self) -> bool {
+	/// Returns `true` if the syncing action has completed.
+	pub fn is_finished(&self) -> bool {
 		matches!(self, SyncingAction::Finished)
 	}
 

substrate/client/network/sync/src/strategy/state.rs

@@ -118,10 +118,11 @@ impl<B: BlockT> StateStrategy<B> {
 		}
 	}
 
-	// Create a new instance with a custom state sync provider.
-	// Used in tests.
-	#[cfg(test)]
-	fn new_with_provider(
+	/// Create a new instance with a custom state sync provider.
+	///
+	/// Note: In most cases, users should use [`StateStrategy::new`].
+	/// This method is intended for custom sync strategies and advanced use cases.
+	pub fn new_with_provider(
 		state_sync_provider: Box<dyn StateSyncProvider<B>>,
 		initial_peers: impl Iterator<Item = (PeerId, NumberFor<B>)>,
 		protocol_name: ProtocolName,
@@ -348,7 +349,7 @@ impl<B: BlockT> StateStrategy<B> {
 		}
 	}
 
-	/// Get actions that should be performed by the owner on [`WarpSync`]'s behalf
+	/// Get actions that should be performed.
 	#[must_use]
 	pub fn actions(
 		&mut self,