Add Telegram rich message helpers

[yashau]

Summary

• Add Bot API 10.1 InputRichMessage and InputRichMessageContent payload helpers aligned with Telegram's documented html, markdown, is_rtl, skip_entity_detection, and rich_message fields.
• Add Richify, RichifyMarkdown, RichifyHTML, ConvertToRichHTML, rich payload options, validation, and Bot API 10.1 limit constants.
• Cover the documented rich Markdown and rich HTML surfaces in tests, including media blocks, tables, footnotes, formulas, details, collages, slideshows, maps, and the draft-only <tg-thinking> block.

Docs reference: https://core.telegram.org/bots/api#rich-message-formatting-options

Verification

• go test ./...
• go vet ./...
• git diff --check
• CGO_ENABLED=1 go test -race ./... could not run locally because this Windows environment has no C compiler on PATH: cgo: C compiler "gcc" not found: exec: "gcc": executable file not found in %PATH%