更新说明：
1、实现了一个栈数据结构，不再单纯使用Vec去表示栈。
2、更新大部分指令的单元测试用例：测试用例迁入到测试模块，并提供了断言测试用例

Release Notes:
Implemented a stack data structure instead of solely using Vec to represent the stack.
Updated most instruction unit test cases: test cases have been migrated to the test module and now include assertion-based test cases.

Full Changelog: https://github.com/dorname/mini-evm/commits/mini-evm-for-study