Add n_c and n_nc for all distributions

[mhostetter]

Fixes #320

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 88.63636% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 78.98%. Comparing base (6f13fb5) to head (d755339).

Files	Patch %	Lines
src/sdr/_detection/_theory.py	85.07%	10 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##           release/0.0.x     #327   +/-   ##
==============================================
  Coverage          78.97%   78.98%           
==============================================
  Files                 59       59           
  Lines               3601     3645   +44     
==============================================
+ Hits                2844     2879   +35     
- Misses               757      766    +9     

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