Implement BlockCache trait for FsBlockDb

zcash_client_backend/CHANGELOG.md

@@ -140,6 +140,15 @@ funds to those addresses. See [ZIP 320](https://zips.z.cash/zip-0320) for detail
 - `zcash_client_backend::wallet::WalletTransparentOutput::from_parts`
   now takes its height argument as `Option<BlockHeight>` rather than
   `BlockHeight`.
+- zcash_client_backend::data_api::chain:
+  - `BlockSource` added Send + Sync trait bounds
+  - `BlockSource::with_blocks` changed to async fn
+  - Changes to `BlockCache` trait:
+    - removed `sync` feature flag so it can be used in `scan_cached_blocks`
+    - all trait methods now return `zcash_client_backend::data_api::chain::error::Error`
+      so implementations may call `BlockSource::with_blocks` and propagate errors correctly.
+  - `scan_cached_blocks` now takes a block cache and a scan range for scanning.
+
 
 ### Removed
 - `zcash_client_backend::data_api`:

zcash_client_backend/Cargo.toml

@@ -71,7 +71,7 @@ orchard = { workspace = true, optional = true }
 sapling.workspace = true
 
 # - Sync engine
-async-trait = { version = "0.1", optional = true }
+async-trait = { version = "0.1" }
 futures-util = { version = "0.3", optional = true }
 
 # - Note commitment trees
@@ -171,15 +171,13 @@ orchard = ["dep:orchard", "dep:pasta_curves", "zcash_keys/orchard"]
 ## Exposes a wallet synchronization function that implements the necessary state machine.
 sync = [
     "lightwalletd-tonic",
-    "dep:async-trait",
     "dep:futures-util",
 ]
 
 ## Exposes a Tor client for hiding a wallet's IP address while performing certain wallet
 ## operations.
 tor = [
     "dep:arti-client",
-    "dep:async-trait",
     "dep:futures-util",
     "dep:http-body-util",
     "dep:hyper",