Stream consumer now splits messages that exceed the platform's
MAX_MESSAGE_LENGTH. When accumulated text grows past the safe limit,
the current message is finalized and a new message is started for the
overflow — same as how normal sends chunk long responses.
Split point prefers line boundaries (rfind newline) for clean breaks.
Works for all platforms (Telegram 4096, Discord 2000, etc.) by reading
the adapter's MAX_MESSAGE_LENGTH at runtime.
Also added a safety net in the Telegram adapter: if edit_message_text
still hits MESSAGE_TOO_LONG (e.g. markdown formatting expansion), it
truncates and returns success so the stream consumer doesn't die.
Co-authored-by: Test <test@test.com>
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