Serialize chat-created model pricing as hashes

[cyphercodes]

What this does

Fixes #784 by converting Model::Info wrapper objects to plain hashes before persisting models created through chat model resolution. This keeps modalities and pricing JSON columns in the same shape as acts_as_model registry sync.

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation
• Performance improvement

Scope check

• I read the Contributing Guide
• This aligns with RubyLLM's focus on LLM communication
• This isn't application-specific logic that belongs in user code
• This benefits most users, not just my specific use case

Required for new features

• I opened an issue before writing code and received maintainer approval
• Linked issue: #___

PRs for new features or enhancements without a prior approved issue will be closed.

Quality check

• I ran overcommit --install and all hooks pass
• I tested my changes thoroughly
  • For provider changes: Re-recorded VCR cassettes with bundle exec rake vcr:record[provider_name]
  • All tests pass: bundle exec rspec
• I updated documentation if needed
• I didn't modify auto-generated files manually (models.json, aliases.json)

AI-generated code

• I used AI tools to help write this code
• I have reviewed and understand all generated code (required if above is checked)

API changes

• Breaking change
• New public methods/classes
• Changed method signatures
• No API changes

Tests

• bundle exec rspec spec/ruby_llm/active_record/acts_as_model_spec.rb
• bundle exec rubocop lib/ruby_llm/active_record/chat_methods.rb spec/ruby_llm/active_record/acts_as_model_spec.rb
• bundle exec rspec spec/ruby_llm/active_record
• Pre-commit overcommit hooks (Gitleaks, TrailingWhitespace, RuboCop, AppraisalUpdate, Flay, RSpec)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.55%. Comparing base (4c24878) to head (70e564d).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #796   +/-   ##
=======================================
  Coverage   87.55%   87.55%           
=======================================
  Files         125      125           
  Lines        5872     5872           
  Branches     1460     1460           
=======================================
  Hits         5141     5141           
  Misses        731      731           

☔ View full report in Codecov by Harness.
📢 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.