chore: 未使用インポートの削除と軽微な警告修正

src/backend/vm_exec.rs

@@ -11,11 +11,10 @@
  * Behavior and public APIs are preserved. This is a pure move/refactor.
  */
 
-use crate::mir::{MirModule, MirFunction, MirInstruction, ValueId, BasicBlockId};
+use crate::mir::{MirModule, MirFunction, MirInstruction, BasicBlockId};
 use crate::box_trait::NyashBox;
 use super::{vm::VM, vm::VMError, vm::VMValue};
 use crate::backend::vm_control_flow::ControlFlow;
-use std::sync::Arc;
 
 impl VM {
     /// Execute a MIR module

src/backend/vm_gc.rs

@@ -6,7 +6,7 @@
  * - Debug prints for roots snapshot and shallow reachability
  */
 
-use super::vm::{VM, VMError, VMValue};
+use super::vm::{VM, VMValue};
 
 impl VM {
     /// Enter a GC root region and return a guard that leaves on drop
@@ -96,4 +96,3 @@ impl VM {
         eprintln!("[GC] depth2_children: total={} top5={:?}", child_count, top);
     }
 }
-

src/backend/vm_instructions/plugin_invoke.rs

@@ -1,5 +1,4 @@
 use crate::mir::ValueId;
-use std::sync::Arc;
 use crate::backend::vm::ControlFlow;
 use crate::backend::{VM, VMError, VMValue};