The newline normalization is the shared chokepoint for every rich send
(sendRichMessage, draft, and editMessageText). Injecting a Markdown hard
break (two trailing spaces) into a GFM table row separator corrupts the
natively-rendered table — the rich path's headline feature. Protect both
fenced code blocks AND pipe-table blocks as bare regions; only prose
between them gets hard breaks. Verified RICH_CONTENT and the existing
rich-table tests stay byte-identical.
Bot API 10.1 sendRichMessage treats a lone newline as a soft break, so
multi-line content joined with "\n".join(lines) — slash-command lists,
etc. — collapses into a single paragraph. Normalize single newlines to
Markdown hard breaks (two trailing spaces) in _rich_message_payload,
leaving paragraph breaks and fenced code blocks untouched.
Fixes#46070
