Add 'sync' command to Python client

[cottsay]

The Python method encompasses both the SYNC and SYNC_PATTERN Assuan commands, choosing the correct one depending on whether a pattern was given.

This includes some mild refactoring:

• in client.c to de-duplicate the arch_list parsing.
• in test_smoke.py to better support the new functionality.

[cottsay]

Looks like the test fixture repositories checked into this repo use zstd compression, which isn't supported by the version of createrepo-c in Ubuntu. I'll need to re-generate them with a compatible compression algorithm and re-sign the metadata.

Back to draft until that has been resolved.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 83.33333% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 48.78%. Comparing base (1a84c85) to head (040deda).
⚠️ Report is 1 commits behind head on cottsay/fixture-repo-compression.

Files with missing lines	Patch %	Lines
src/python/client.c	83.33%	3 Missing and 3 partials ⚠️

Additional details and impacted files

@@                         Coverage Diff                          @@
##           cottsay/fixture-repo-compression      #29      +/-   ##
====================================================================
+ Coverage                             42.67%   48.78%   +6.11%     
====================================================================
  Files                                    20       20              
  Lines                                  2615     2642      +27     
  Branches                                532      538       +6     
====================================================================
+ Hits                                   1116     1289     +173     
+ Misses                                 1244     1047     -197     
- Partials                                255      306      +51     

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[cottsay]

Alright, this can be reviewed now, but I'm keeping it in draft until #30 has been merged.