fix(rfq): support balance error codes

[cesarenaldi]

Summary

• add the latest Combos RFQ balance, allowance, and pre-execution reservation error codes to the public RFQ error enum
• extend existing RFQ websocket rejection coverage to use the new codes when integration credentials are available

Linear: DEV-265

Verification

• uv run pytest tests/integration/test_rfq.py -k quote_rejection -q (skipped locally: requires POLYMARKET_PRIVATE_KEY/POLYMARKET_DEPOSIT_WALLET)
• uv run ruff check src tests
• uv run pyright

---

Note

Low Risk
Enum and test-only changes with no RFQ session or wire-protocol behavior changes beyond recognizing new error code strings.

Overview
Extends the public RfqErrorCode enum with three Combos RFQ wire codes: ALLOWANCE_VALIDATION_FAILED, BALANCE_VALIDATION_FAILED, and PRE_EXECUTION_BALANCE_RESERVATION_FAILED, so clients can distinguish balance/allowance/reservation failures from generic quote errors.

The RFQ websocket quote-rejection integration test is parametrized over those codes and now asserts RfqQuoteRejectedError.code matches the server RFQ_ERROR payload (previously only INVALID_QUOTE was exercised).

^{Reviewed by Cursor Bugbot for commit 2b71c99. Bugbot is set up for automated code reviews on this repo. Configure here.}