feat(rfq): expose confirmed trade broadcasts

[shazam8253]

Summary

• expose confirmed public RFQ_TRADE websocket frames as typed RfqTradeEvent session events
• use the finalized public wire contract: requester_id, combo condition_id, legs, direction, side, price, size, and execution timestamp
• intentionally omit the settlement transaction hash from public trade events; makers still receive it through their private RFQ_EXECUTION_UPDATE

Scope

• implemented independently from main; no dependency on Cesare's reverted branch or commits
• follows the established RFQ SDK model, parser, export, and local-websocket integration-test conventions
• pairs with https://github.com/Polymarket/combos-rfq/pull/110

Verification

• ruff format --check .
• ruff check .
• strict Pyright over changed RFQ files
• direct RFQ_TRADE parser smoke check
• GitHub Actions pending

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Note

Low Risk
Additive RFQ event type and websocket parsing with no changes to quoting, signing, or settlement paths.

Overview
RFQ quoter websocket sessions now surface public RFQ_TRADE frames as typed RfqTradeEvent items on the existing event stream, alongside quote, confirmation, and execution-update events.

Each trade event carries the finalized public wire fields (requester_id, combo condition_id, legs, direction, side, price, size, executed_at) with e6 decimals converted to Decimal. Settlement tx_hash is intentionally omitted from the public trade shape; makers still get it via private RfqExecutionUpdateEvent.

The internal quoter parses RFQ_TRADE in _on_message, RfqTradeEvent is exported from the package, and integration tests cover standalone trade broadcast reception and trade frames interleaved in the quote/confirm flow.

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