feat: 添加 R_PUSH指令类

- 新增 RPushCommand 类实现 Command 接口，用于处理引用类型推入操作
- 支持将字符串字面量等引用类型数据推入操作栈

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

@@ -0,0 +1,63 @@
+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 RPushCommand} class implements the {@link Command} interface and represents the
+ * reference push instruction ({@code R_PUSH}) in the virtual machine.
+ *
+ * <p>
+ * This instruction pushes a reference object, such as a String literal, onto the operand stack.
+ * </p>
+ *
+ * <p>Instruction format: {@code R_PUSH <literal>}</p>
+ * <ul>
+ *   <li>{@code <literal>}: The reference value (e.g., string) to be pushed onto the stack.
+ *   If the literal contains spaces, all parts after {@code R_PUSH} are joined into a single string.</li>
+ * </ul>
+ *
+ * <p>Behavior:</p>
+ * <ul>
+ *   <li>Checks that the instruction has at least one parameter after the operator.</li>
+ *   <li>Concatenates all parameters after {@code R_PUSH} into a single string (separated by spaces).</li>
+ *   <li>Pushes the resulting string as a reference object onto the operand stack.</li>
+ *   <li>Increments the program counter to the next instruction.</li>
+ *   <li>Throws an {@code IllegalStateException} if the instruction is missing required parameters.</li>
+ * </ul>
+ */
+public final class RPushCommand implements Command {
+
+    /**
+     * Executes the {@code R_PUSH} instruction, pushing a reference (such as a string literal)
+     * onto the operand stack.
+     *
+     * @param parts The instruction parameters. {@code parts[0]} is the operator ("R_PUSH"),
+     *              {@code parts[1..]} are the parts of the literal to be concatenated and pushed.
+     * @param pc    The current program counter value, indicating the instruction address being executed.
+     * @param stack The operand stack manager. The literal will be pushed onto this stack.
+     * @param lvs   The local variable store. (Not used in this instruction.)
+     * @param cs    The call stack manager. (Not used in this instruction.)
+     * @return The next program counter value ({@code pc + 1}), pointing to the next instruction.
+     * @throws IllegalStateException if the instruction is missing required parameters.
+     */
+    @Override
+    public int execute(String[] parts, int pc,
+                       OperandStack stack,
+                       LocalVariableStore lvs,
+                       CallStack cs) {
+
+        if (parts.length < 2)
+            throw new IllegalStateException("R_PUSH missing parameter");
+
+        StringBuilder sb = new StringBuilder();
+        for (int i = 1; i < parts.length; i++) {
+            if (i > 1) sb.append(' ');
+            sb.append(parts[i]);
+        }
+        stack.push(sb.toString());
+        return pc + 1;
+    }
+}