Support request customization for all API endpoints

- Introduced `extra_query`, `extra_headers`, `extra_body`, and `timeout`
  parameters across synchronous and asynchronous methods for enhanced
  flexibility in API integrations.
- Added a validation check to prevent combining JSON payloads with
  multipart file uploads.
- Updated client methods for file handling, downloads, and conversions
  to include optional request customizations.
- Extended tests to cover new request customization capabilities and
  ensure proper handling of custom parameters in both sync and async
  clients.

Author: datalogics-kam