Convert trades.csv to inline JSON and remove CSV loading code path

[R7L208]

• Inline trades.csv data directly into ml_tests.json as a JSON array
• Remove trades.csv file
• Simplify TestDataFrameBuilder.df_data() to only handle list data
• Remove unused pandas import from base.py

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.57%. Comparing base (f022563) to head (417bc6b).
⚠️ Report is 147 commits behind head on v0.2-integration.

Additional details and impacted files

@@                  Coverage Diff                  @@
##           v0.2-integration     #451       +/-   ##
=====================================================
- Coverage             85.46%   71.57%   -13.90%     
=====================================================
  Files                     6       29       +23     
  Lines                   757     2621     +1864     
  Branches                156      425      +269     
=====================================================
+ Hits                    647     1876     +1229     
- Misses                   92      589      +497     
- Partials                 18      156      +138     

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