fix: make model_from_dict model parameter positional-only

[cofin]

Summary

• Make model parameter positional-only (/) in model_from_dict() to prevent TypeError when the data dict contains a "model" key
• Update all call sites in service layer to use positional form

Closes #668

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.17%. Comparing base (e306121) to head (f48ebea).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #673   +/-   ##
=======================================
  Coverage   81.17%   81.17%           
=======================================
  Files          99       99           
  Lines        7990     7990           
  Branches     1079     1079           
=======================================
  Hits         6486     6486           
  Misses       1180     1180           
  Partials      324      324           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.