feat: 添加 R_STORE指令的实现

- 新增 RStoreCommand 类，实现 Command接口
- 添加 R_STORE指令的执行逻辑
- 更新虚拟机的指令集，支持 R_STORE 指令

src/main/java/org/jcnc/snow/vm/commands/ref/control/RStoreCommand.java

@@ -0,0 +1,58 @@
+package org.jcnc.snow.vm.commands.ref.control;
+
+import org.jcnc.snow.vm.interfaces.Command;
+import org.jcnc.snow.vm.module.CallStack;
+import org.jcnc.snow.vm.module.LocalVariableStore;
+import org.jcnc.snow.vm.module.OperandStack;
+
+/**
+ * The {@code RStoreCommand} class implements the {@link Command} interface and represents the
+ * reference store instruction ({@code R_STORE}) in the virtual machine.
+ *
+ * <p>
+ * This instruction pops a reference object from the top of the operand stack
+ * and stores it in the local variable table at the specified slot index of the current stack frame.
+ * </p>
+ *
+ * <p>Instruction format: {@code R_STORE <slot>}</p>
+ * <ul>
+ *   <li>{@code <slot>}: The index in the local variable table where the reference will be stored.</li>
+ * </ul>
+ *
+ * <p>Behavior:</p>
+ * <ul>
+ *   <li>Parses the slot index from the instruction parameters.</li>
+ *   <li>Pops a reference object from the operand stack.</li>
+ *   <li>Stores the popped reference object into the local variable table of the current stack frame at the specified slot.</li>
+ *   <li>Increments the program counter to the next instruction.</li>
+ *   <li>If the operand stack is empty, a {@code java.util.EmptyStackException} may be thrown.</li>
+ * </ul>
+ */
+public final class RStoreCommand implements Command {
+
+    /**
+     * Executes the {@code R_STORE} instruction, storing a reference object from the top of the operand stack
+     * into the local variable table of the current stack frame.
+     *
+     * @param parts The instruction parameters. {@code parts[0]} is the operator ("R_STORE"),
+     *              {@code parts[1]} is the slot index.
+     * @param pc    The current program counter value, indicating the instruction address being executed.
+     * @param stack The operand stack manager. The reference object will be popped from this stack.
+     * @param lvs   The local variable store. (Not used directly, as the store from the current stack frame is used.)
+     * @param cs    The call stack manager. The reference will be stored in the local variable store of the top stack frame.
+     * @return The next program counter value ({@code pc + 1}), pointing to the next instruction.
+     * @throws NumberFormatException if the slot parameter cannot be parsed as an integer.
+     * @throws java.util.EmptyStackException if the operand stack is empty when popping.
+     */
+    @Override
+    public int execute(String[] parts, int pc,
+                       OperandStack stack,
+                       LocalVariableStore lvs,
+                       CallStack cs) {
+
+        int slot = Integer.parseInt(parts[1]);
+        Object v = stack.pop();
+        cs.peekFrame().getLocalVariableStore().setVariable(slot, v);
+        return pc + 1;
+    }
+}