Optimizations for Shamir-based Protocol

[f7ed]

Pull Request

What problem does this PR solve?

主要修改包括：
libspu/mpc/utils/gfmp_ops.cc

•        修改gfmp_reconstruct_shamir_shares中的公式
•        增加batch_inversion操作，以及相应的gtest
  ‎libspu/mpc/shamir/arithmetic.cc
•        增加MulAAP接口（即合并MulAA + A2P运算），以及相应的gtest；
•        增加PRZS（随机零分享）接口；
•        修改P2A协议：random shamir sharing -> public values as sharing；
  libspu/mpc/shamir/boolean.cc
•        修改B2P协议：-> B2A + A2P
•        修改B2V协议：-> B2A + A2V
  libspu/mpc/shamir/conversion.cc
•        用batch_inversion优化rand_bits
•        利用梅森素数的性质优化rand_bits协议
•        删除rand_bits_pair协议
•        利用梅森素数的性质优化solved_bits
•        新增gen_prefix_mul_share接口，生成用于计算prefix_mult所需的random pairs
•        利用gen_prefix_mul重新实现prefix_mul协议，测试MsbA接口
•        利用重新实现的prefix_mul接口优化bit_it_ap协议
•        优化unbounded_carries协议
•        优化A2B协议
•        新增MultAATrunc协议，即定点小数乘法协议

Issue Number: Fixed #

Possible side effects?

• Performance:

• Backward compatibility:

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