[FEAT] Sign expression implemtation

[sherlockbeard]

implementation for sign resolves #1917

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.70%. Comparing base (afd6a75) to head (cd8ed01).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2037      +/-   ##
==========================================
- Coverage   84.74%   84.70%   -0.05%     
==========================================
  Files          62       62              
  Lines        6803     6811       +8     
==========================================
+ Hits         5765     5769       +4     
- Misses       1038     1042       +4     

Files	Coverage Δ
daft/expressions/expressions.py	91.57% <100.00%> (+0.05%)	⬆️
daft/series.py	93.16% <100.00%> (+0.02%)	⬆️

... and 2 files with indirect coverage changes

[samster25]

Thanks @sherlockbeard for taking this on!
@colin-ho Can you take a look?

[colin-ho]

Thanks @sherlockbeard for taking this on! @colin-ho Can you take a look?

Thanks @sherlockbeard for this PR! Just left a few comments :)

[colin-ho]

Awesome stuff @sherlockbeard!! Thanks for this contribution :)

[jaychia]

Congrats on your first PR @sherlockbeard !! 🔥