Encode build_options in base64

[pmachapman]

Partial fix for #966.

Requires: sillsdev/machine.py#330.

I will implement build_option constraints separately in another PR, as those will be implemented at the API boundary.

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This change is 

[codecov-commenter]

Codecov Report

❌ Patch coverage is 66.66667% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.53%. Comparing base (db04610) to head (ee83242).

Files with missing lines	Patch %	Lines
...ared/Services/StatisticalClearMLBuildJobFactory.cs	0.00%	5 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #992   +/-   ##
=======================================
  Coverage   65.53%   65.53%           
=======================================
  Files         387      387           
  Lines       21743    21755   +12     
  Branches     2769     2769           
=======================================
+ Hits        14249    14257    +8     
- Misses       6454     6458    +4     
  Partials     1040     1040           

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