Add Gold codes and preferred pairs

[mhostetter]

• Closes Add sdr.preferred_pairs() #384
• Closes Add sdr.is_preferred_pair() #386
• Closes Add sdr.gold() #274

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 87.50000% with 15 lines in your changes missing coverage. Please review.

Project coverage is 79.59%. Comparing base (507c802) to head (9547ab2).

Files	Patch %	Lines
src/sdr/_sequence/_correlation.py	74.46%	12 Missing ⚠️
src/sdr/_sequence/_maximum.py	96.82%	2 Missing ⚠️
src/sdr/_sequence/_symbol_mapping.py	90.00%	1 Missing ⚠️

Additional details and impacted files

@@                Coverage Diff                @@
##           release/0.0.x     #387      +/-   ##
=================================================
+ Coverage          79.41%   79.59%   +0.18%     
=================================================
  Files                 63       63              
  Lines               3842     3931      +89     
=================================================
+ Hits                3051     3129      +78     
- Misses               791      802      +11     

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