feat: add sort and order params to conversations list API

[TsainGra]

• Added support for sorting by created_at or updated_at fields (default: created_at)
• Added support for ascending or descending order (default: desc)
• Updated user router, controller, and service to handle new parameters
• Fixed line length issues to comply with linting rules

Closes #359

Summary by CodeRabbit

• New Features

  • Added support for sorting and ordering conversations when retrieving a user's conversation list. Users can now specify sort field ("created_at" or "updated_at") and order ("asc" or "desc") via new query parameters.

• Enhancements

  • Improved error handling and logging for conversation retrieval operations.