Implement SQiSW decomposition

[ecpeterson]

Huang et al. recently produced an optimal compilation technique for XY(pi/4) = \sqrt{ISWAP}, which quilc still compiles using numerical search, despite this being a native interaction on certain Rigetti devices. Implementing this would be a significant improvement in compiler output on pertinent architectures.

https://arxiv.org/abs/2105.06074