[FEAT] adding floor function

[chandbud5]

Adding floor function. Resolves - #1910

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.95%. Comparing base (cc7b957) to head (590d59b).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1960      +/-   ##
==========================================
+ Coverage   83.90%   83.95%   +0.05%     
==========================================
  Files          55       55              
  Lines        6112     6125      +13     
==========================================
+ Hits         5128     5142      +14     
+ Misses        984      983       -1     

Files	Coverage Δ
daft/expressions/expressions.py	91.33% <100.00%> (+0.10%)	⬆️
daft/series.py	93.15% <100.00%> (+0.07%)	⬆️

... and 2 files with indirect coverage changes

[samster25]

Amazing! Thanks for knocking this out :)