Add support for Telegram Bot API 7.3

This commit implements the features introduced in the Telegram Bot API 7.3 update (May 6, 2024).

Key changes include:

• Poll Enhancements:
  • New InputPollOption entity.
  • Added question_entities to Poll and text_entities to PollOption.
  • Updated sendPoll method with new options and question_entities parameters.
• Chat and getChat Refactoring:
  • New ChatFullInfo entity with max_reaction_count and other getChat-specific fields.
  • getChat method now returns ChatFullInfo.
• Miscellaneous Updates:
  • New ChatBackground, BackgroundType, and BackgroundFill entities.
  • Added chat_background_set to Message entity.
  • Added via_join_request to ChatMemberUpdated entity.
  • Added live_period to editMessageLiveLocation method.

Updated CHANGELOG.md and library version to 1.0.3.