[FEA] Audit regexp/cast code to see if we can use more non-capture groups

[andygrove]

Is your feature request related to a problem? Please describe.
#6468 is a good example of a simple optimization by using non-capture groups instead of capture groups in a regexp call. We should see if there are other places where we can do this (I'm certain there are plenty of examples in the GpuCast code).

Describe the solution you'd like
Audit the code and use non-capture groups where possible.

Describe alternatives you've considered
None

Additional context
None

[sameerz]

Related cudf issue rapidsai/cudf#11663