feat: save to BMA json format

[ReubenJ]

Checklist

• I am following the contributing guidelines
• Tests are passing
• Lint workflow is passing
• Docs were updated and workflow is passing

[codecov]

Codecov Report

❌ Patch coverage is 89.90826% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.66%. Comparing base (874c540) to head (0c30750).
⚠️ Report is 22 commits behind head on main.

Files with missing lines	Patch %	Lines
src/qualitative_networks.jl	81.31%	17 Missing ⚠️
src/io/bma.jl	96.06%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #44      +/-   ##
==========================================
- Coverage   98.40%   93.66%   -4.74%     
==========================================
  Files           3        3              
  Lines         251      379     +128     
==========================================
+ Hits          247      355     +108     
- Misses          4       24      +20     

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