Image generation now accepts file IDs; file URLs and filtering added

What's Changed

• Add Imagine file storage & file-ID inputs to image/video generation by @Omar-V2 in https://github.com/xai-org/xai-sdk-python/pull/160
• Add public file URLs and list filtering to the files client by @Omar-V2 in https://github.com/xai-org/xai-sdk-python/pull/161
• Add new grok imagine models to types/model.py for editor autocomplete by @Omar-V2 in https://github.com/xai-org/xai-sdk-python/pull/162
• Prepare to release v1.16.0 of the xAI Python SDK by @Omar-V2 in https://github.com/xai-org/xai-sdk-python/pull/164

Full Changelog: https://github.com/xai-org/xai-sdk-python/compare/v1.15.0...v1.16.0