[FEAT] Add str.extract() function

[colin-ho]

str.extract(pattern: str | Expression, index : int) Extracts the regex match group from each string in a string column. If index is 0, the entire match is returned, otherwise the specified group is returned.

https://ibis-project.org/reference/expression-strings#ibis.expr.types.strings.StringValue.re_extract

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 84.72%. Comparing base (e96266d) to head (fac2c2a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2020      +/-   ##
==========================================
+ Coverage   84.68%   84.72%   +0.03%     
==========================================
  Files          62       62              
  Lines        6779     6787       +8     
==========================================
+ Hits         5741     5750       +9     
+ Misses       1038     1037       -1     

Files	Coverage Δ
daft/expressions/expressions.py	91.62% <100.00%> (+0.05%)	⬆️
daft/series.py	92.98% <80.00%> (-0.15%)	⬇️

... and 1 file with indirect coverage changes

[kevinzwang]

Some comments but overall code looks good!