fix: revert layers to internal to fix public-property-of-internal-type error

Qwen3TransformerBlock and Qwen3MoeDecoderLayer are internal types.
Declaring public let layers of those types violates Swift's access
control rules. callCapturing() is defined in the same module so can
access internal layers directly — no need to expose them publicly.

Author: Aegis-AI

Libraries/MLXLLM/Models/Qwen3.swift

@@ -147,7 +147,7 @@ public class Qwen3ModelInner: Module, LayerPartitionable {
     public var totalLayerCount: Int { layers.count }
     @ModuleInfo(key: "embed_tokens") public var embedTokens: Embedding
 
-    public let layers: [Qwen3TransformerBlock]
+    let layers: [Qwen3TransformerBlock]
     let norm: RMSNorm
 
     public init(_ args: Qwen3Configuration) {

Libraries/MLXLLM/Models/Qwen3MoE.swift

@@ -198,7 +198,7 @@ public class Qwen3MoEModelInner: Module, LayerPartitionable, StreamableMoE {
 
     @ModuleInfo(key: "embed_tokens") public var embedTokens: Embedding
 
-    public let layers: [Qwen3MoeDecoderLayer]
+    let layers: [Qwen3MoeDecoderLayer]
     let norm: RMSNorm
     let args: Qwen3MoEConfiguration