Two kill-switch tests for the new inline-keyboards path. Neither is
flashy — they just make sure the next unrelated refactor can't quietly
regress two narrow contracts the PR relies on.
1. TelegramChannel._build_keyboard returns None whenever
TelegramConfig.inline_keyboards is False, even if buttons are
supplied. The flag defaults off; if someone ever flips that default
the change should fail this test before it reaches prod bots.
2. MessageTool rejects malformed `buttons` payloads (non-list, mixed
list/str row, non-str label, None label) up front instead of
letting them slip into the channel layer where Telegram would
silently 400 the send. Parametrized over four shapes the guard
needs to reject.
No production code touched.
Made-with: Cursor
