Add on-demand history sync request

[osyris]

The gap

A linked device has no server-side archive to read from: WhatsApp hands over a
shallow slice of history once at pairing time and never resends it. Anything
older lives on the phone.

whatsmeow covers this with BuildHistorySyncRequest + SendPeerMessage, but
neither is bound in neonize, so from Python there is currently no way to reach
messages older than whatever arrived at pairing. In practice that means a few
messages per chat.

The change

Exposes the pair as one call.

• goneonize: RequestHistorySync export, following the surrounding pattern
  (ProtoReturnV3, clients, utils.DecodeJidProto, SendMessageReturnFunction)
• _binder.py: ctypes signature
• client.py: NewClient.request_history_sync(chat, message_id, from_me, timestamp, count=50)

The request is anchored on a message the caller already holds; the phone answers
with up to count messages immediately preceding it. As documented upstream, the
answer is asynchronous — it arrives as a HistorySyncEv whose
Data.syncType is ON_DEMAND, not as this call's return value. Paging further
back is re-anchoring on the oldest message held and calling again.

@client.event(HistorySyncEv)
def on_history(_, ev):
    if ev.Data.syncType == 6:  # ON_DEMAND
        ...

client.request_history_sync(chat_jid, oldest_id, oldest_from_me, oldest_ts, 50)

Two caveats worth knowing, both inherent to the mechanism rather than to this
binding: the phone must be online to answer, and count=50 is what whatsmeow
recommends per request.

Testing

Verified against a live linked account.

• A single request returns exactly count messages, roughly 4s round trip.
• Paging back repeatedly works: 20 consecutive rounds of 50 all answered in
  full, taking one group chat from 728 to 2327 messages and its oldest message
  from 2026-06-10 back to 2025-11-29.
• Continuing to the end of available history, the answers degrade the way you
  would expect at a real boundary: a short chunk (42 of 50) followed by an
  immediate empty answer. Final state for that chat was 3619 messages spanning a
  full year, up from 728 at pairing.
• The public Python method was exercised end to end on top of this branch's own
  build: request accepted, syncType=6, 50 messages returned.

No existing exports or signatures are touched; the change is additive.