Fix acts_as_tool_call message: option (#514)

[saurabh-sikchi]

What this does

Fixes cleanup_orphaned_tool_results ignoring custom association names configured via acts_as_tool_call message: and acts_as_message tool_calls: options.

The bug: When using custom association names like acts_as_tool_call message: :llm_message, the cleanup method called hardcoded .message and .tool_calls instead of the configured association names, causing NoMethodError.

The fix: Use message_association and tool_calls_association methods, which respect the configured names.

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

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)

API changes

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

Related issues

#514