Allow raising cyclotomics to a UPoly

[SoongNoonien]

In preparation to #261 we should allow raising generic cyclotomics to more general powers.

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.87%. Comparing base (dca1ec2) to head (ca37e3a).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/GenericCyclotomics.jl	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #263      +/-   ##
==========================================
- Coverage   95.96%   95.87%   -0.10%     
==========================================
  Files          12       12              
  Lines         843      848       +5     
==========================================
+ Hits          809      813       +4     
- Misses         34       35       +1     

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