feat: support Telegram Rich Messages

[aleksesipenko]

Telegram Bot API 10.1/10.2 introduced Rich Messages.

Proposal:

• expose native rich-message sending with HTML or Markdown;
• expose streaming rich-message drafts;
• return rich_message when reading messages;
• cover payload construction and result serialization with tests.

This uses Telethon's existing InputRichMessage* and messages.SendMessageRequest support, while preserving existing plain-message tools.

Reference: https://core.telegram.org/bots/api#rich-messages