fix(gateway): escape Telegram chunk indicators for MarkdownV2

[starlash7]

Summary

• escape the trailing chunk indicator added to multi-part Telegram messages before sending with MarkdownV2
• keep the shared chunking behavior unchanged for other adapters
• add a regression test covering chunked formatted Telegram responses

Testing

• ./.venv/bin/python -m pytest tests/gateway/test_telegram_format.py tests/gateway/test_platform_base.py
• ./.venv/bin/python -m pytest tests/gateway/test_telegram_documents.py -k send_document_success -q

Closes #1456

[teknium1]

Thanks for the contribution! This fix was already merged independently via PR #1478 — the chunk indicator escaping is now inlined in send() at line 325-331 of telegram.py, with test coverage at test_send_escapes_chunk_indicator_for_markdownv2. Closing as redundant.