feat(spider-scheduler): Add round-robin scheduler core implementation.

components/spider-scheduler/Cargo.toml

@@ -10,12 +10,14 @@ path = "src/lib.rs"
 [dependencies]
 async-channel = "2.3.1"
 async-trait = "0.1.89"
+serde = { version = "1.0.228", features = ["derive"] }
 spider-core = { path = "../spider-core" }
 spider-proto-rust = { path = "../spider-proto-rust" }
 thiserror = "2.0.18"
-tokio = { version = "1.52.3", features = ["sync", "time"] }
+tokio = { version = "1.52.3", features = ["macros", "rt", "sync", "time"] }
 tokio-util = "0.7.18"
 tonic = "0.12.3"
+tracing = { version = "0.1.41", default-features = false, features = ["std"] }
 
 [dev-dependencies]
 anyhow = "1.0.102"

components/spider-scheduler/src/core.rs

@@ -16,12 +16,12 @@ use crate::{
 /// share the same runtime entry point.
 #[async_trait]
 pub trait SchedulerCore: Send {
-    /// The storage client used by the core to poll and read for placement decisions.
-    type StorageClient: SchedulerStorageClient;
-
     /// The dispatch sink the core writes assignments to.
     type Sink: DispatchQueueSink;
 
+    /// The storage client used by the core to poll and read for placement decisions.
+    type StorageClient: SchedulerStorageClient;
+
     /// Runs the scheduling loop until `cancellation_token` is triggered.
     ///
     /// The core polls the inbound queue through `storage_client`, applies its scheduling algorithm,
@@ -39,7 +39,7 @@ pub trait SchedulerCore: Send {
     ///
     /// Returns a [`SchedulerError`] instance indicating an irrecoverable error.
     async fn run(
-        &mut self,
+        self,
         storage_client: Self::StorageClient,
         sink: Self::Sink,
         cancellation_token: tokio_util::sync::CancellationToken,

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

@@ -0,0 +1,3 @@
+mod round_robin;
+
+pub use round_robin::*;