implement sSQRTXX, sInvSQRTXX, sSQRTYY, sInvSQRTYY

[Fe-r-oz]

This PR completes all the last remaining two qubit gates that were missing from https://github.com/quantumlib/Stim/blob/main/doc/gates.md.

• The code is properly formatted and commented.
• Substantial new functionality is documented within the docs.
• All new functionality is tested.
• All of the automated tests on github pass.

[Fe-r-oz]

The PR is ready. There will be merge conflicts after merging #336, so after that is merged, I will update this and request for review. Thank you!

This PR along with #336 completes all the two qubit symbolic gates w.r.t to stim so maybe #45 can be considered for closing now?

For stim reference

SQRTXX: https://github.com/quantumlib/Stim/blob/main/doc/gates.md#SQRT_XX
InvSQRTXX: https://github.com/quantumlib/Stim/blob/main/doc/gates.md#the-sqrt_xx_dag-gate

SQRTYY: https://github.com/quantumlib/Stim/blob/main/doc/gates.md#the-sqrt_yy-gate
InvSQRTYY: https://github.com/quantumlib/Stim/blob/main/doc/gates.md#the-sqrt_yy_dag-gate

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.48%. Comparing base (f3eb7cd) to head (4f4b2fe).
Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #368      +/-   ##
==========================================
+ Coverage   82.42%   82.48%   +0.05%     
==========================================
  Files          70       70              
  Lines        4580     4584       +4     
==========================================
+ Hits         3775     3781       +6     
+ Misses        805      803       -2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[Fe-r-oz]

Let's add the remaining of these as well @Krastanov, Thanks!

This PR completes the set of named two-qubits gates w.r.t to stim.

[Krastanov]

thank you, this is great to have