feat(sol): sign gadget

[stuarttimwhite]

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Rationale for this change

We need sign_expr for group by

What changes are included in this PR?

New sign_expr in solidity.

Are these changes tested?

Yes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.71%. Comparing base (95439e3) to head (31acbc4).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #860      +/-   ##
==========================================
- Coverage   96.71%   96.71%   -0.01%     
==========================================
  Files         332      332              
  Lines       60150    60125      -25     
==========================================
- Hits        58176    58149      -27     
- Misses       1974     1976       +2     

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