v2: add actor-based serialization for EmbeddingServer, fix stability for ASCII text

Sources/EmbeddingServer/EmbeddingServerMain.swift

@@ -23,6 +23,9 @@ struct EmbeddingServerMain {
 
         print("EmbeddingGemma loaded (\(layers) layers, hidden=\(hiddenSize))")
 
+        // Use actor to serialize access to embedModel
+        let embedder = Embedder(model: embedModel)
+
         let router = Router()
 
         router.get("/") { _, _ in
@@ -49,10 +52,8 @@ struct EmbeddingServerMain {
 
             var embeddings: [[String: Any]] = []
             for (i, text) in inputs.enumerated() {
-                let t0 = Date()
-                let embedding = try embedModel.embed(text: text)
-                let ms = Int(Date().timeIntervalSince(t0) * 1000)
-                embeddings.append(["object": "embedding", "index": i, "embedding": embedding, "usage_ms": ms])
+                let result = try await embedder.embed(text: text)
+                embeddings.append(["object": "embedding", "index": i, "embedding": result.embedding, "usage_ms": result.ms])
             }
 
             let id = UUID().uuidString
@@ -75,3 +76,23 @@ struct EmbeddingServerMain {
         try await app.run()
     }
 }
+
+struct EmbeddingResult {
+    let embedding: [Float]
+    let ms: Int
+}
+
+actor Embedder {
+    private let model: EmbeddingGemmaModel
+    
+    init(model: EmbeddingGemmaModel) {
+        self.model = model
+    }
+    
+    func embed(text: String) throws -> EmbeddingResult {
+        let t0 = Date()
+        let embedding = try model.embed(text: text)
+        let ms = Int(Date().timeIntervalSince(t0) * 1000)
+        return EmbeddingResult(embedding: embedding, ms: ms)
+    }
+}