add libspu/mpc/swift (only for code recivew)

[lwxxxxxxx]

Pull Request

What problem does this PR solve?

在libspu/mpc目录中增加 swift 目录，实现了MPC 协议 SWIFT (ref: https://www.usenix.org/conference/usenixsecurity21/presentation/koti). 中的部分算子（Arithmetic 和 Boolean），且在protocol_test中只验证了算子正确性，未进行verifyCost。

Issue Number: Fixed #

Possible side effects?

• Performance:

• Backward compatibility:

[github-actions]

Thank you for your submission, we really appreciate it. Like many open-source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution. You can sign the CLA by just posting a Pull Request Comment same as the below format.

---

I have read the CLA Document and I hereby sign the CLA

---

lwxxxxxxx seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You can retrigger this bot by commenting recheck in this Pull Request. Posted by the CLA Assistant Lite bot.}

[lwxxxxxxx]

I have read the CLA Document and I hereby sign the CLA

[anakinxc]

@fionser @deadlywing mind take a look? Thanks

[fionser]

超纲