Add grpc impl of scheduler's storage client

Author: sitaowang1998

components/spider-scheduler/Cargo.toml

@@ -10,5 +10,7 @@ path = "src/lib.rs"
 [dependencies]
 async-trait = "0.1.89"
 spider-core = { path = "../spider-core" }
+spider-proto-rust = { path = "../spider-proto-rust" }
 thiserror = "2.0.18"
+tonic = "0.12.3"
 tokio-util = "0.7.18"

components/spider-scheduler/src/error.rs

@@ -12,6 +12,25 @@ pub enum StorageClientError {
     /// No job with the requested identifier exists.
     #[error("job not found: {0:?}")]
     JobNotFound(JobId),
+
+    /// The scheduler's storage session is stale.
+    #[error("stale storage session: {storage_session:?}")]
+    StaleSession {
+        /// Storage's current session ID.
+        storage_session: SessionId,
+    },
+
+    /// The storage server returned an invalid input error.
+    #[error("invalid storage request: {0}")]
+    InvalidInput(String),
+
+    /// The storage server returned an otherwise-uncategorized error.
+    #[error("storage server error: {0}")]
+    Server(String),
+
+    /// The storage transport failed or returned malformed data.
+    #[error("storage transport error: {0}")]
+    Transport(String),
 }
 
 /// Errors returned by the scheduler runtime and its components.

components/spider-scheduler/src/grpc/mod.rs

@@ -0,0 +1,5 @@
+//! gRPC-backed scheduler client implementations.
+
+mod storage_client;
+
+pub use storage_client::GrpcSchedulerStorageClient;