fix: initialize Baozi order book resolver queues

[iccccccccccccc]

Fixes #261

Changes

• Replace the guarded orderBookResolvers.get(...)! push path with an explicit queue initializer.
• Add a regression test so Baozi websocket resolver queueing does not reintroduce the non-null assertion pattern.
• Fix the Python exchange generator's underscore handling so polymarket_us is exported as PolymarketUS; this keeps the existing exchange drift gate green.
• Preserve the generated SDK fetchOrderBook special handling for params-without-limit and historical range responses.
• Refresh API reference output from the existing generator.

Verification

• npm --workspace=pmxt-core test -- --runTestsByPath test/pipeline/baozi-websocket-resolvers.test.ts --runInBand
• npx tsc -p core/tsconfig.json --noEmit
• node core/scripts/check-exchange-drift.js
• node sdks/typescript/scripts/generate-client-methods.js; git diff --exit-code sdks/typescript/pmxt/client.ts
• node sdks/python/scripts/generate-client-methods.js; git diff --exit-code sdks/python/pmxt/client.py
• python -m py_compile sdks/python/pmxt/_exchanges.py sdks/python/pmxt/__init__.py sdks/python/pmxt/client.py
• git diff --check

[realfishsam]

PR Review: PASS (NOT VERIFIED)

What This Does

Three fixes bundled in one PR: (1) eliminates a non-null assertion (!) on a Map.get() in the Baozi WebSocket order book resolver queue by extracting a getOrderBookQueue helper method, (2) fixes the Python exchange generator so polymarket_us produces the class name PolymarketUS instead of Polymarket_us, and (3) adds hardcoded fetchOrderBook overrides in both SDK client generators to handle the params-without-limit positional arg gap and OrderBook[] historical range responses.

Blast Radius

• Baozi exchange: WebSocket order book watching path only. The getOrderBookQueue refactor is semantically identical to the old code but removes the ! assertion. No behavior change.
• Python SDK: Polymarket_us class renamed to PolymarketUS in _exchanges.py and __init__.py. This is a breaking change for existing Python users of pmxt.Polymarket_us().
• SDK generators (both TS + Python): fetchOrderBook now has a hardcoded override in the generator to handle OrderBook | OrderBook[] return type and params-without-limit gap. The generated client files already match.
• API_REFERENCE.md (both SDKs): Regenerated from current BaseExchange.ts -- includes incidental changes like testDummyMethod -> close and FetchOrderBookParams type documentation.

Test Results

• Build: NOT RUN (permission issue in sandbox)
• Unit tests: NOT RUN (permission issue in sandbox)

Findings

1. Breaking change: Polymarket_us -> PolymarketUS (sdks/python/pmxt/_exchanges.py:368, init.py:20,146) -- Any Python user doing pmxt.Polymarket_us() will get an ImportError after upgrading. The sidecar routing key (exchange_name="polymarket_us") is unaffected. Given this exchange is relatively new (added recently via 5c000a8), the blast radius may be small, but it is technically a semver-breaking rename. Consider whether a deprecation alias is warranted.

2. any[] in fetchOrderBook TS generator (sdks/typescript/scripts/generate-client-methods.js:389) -- The hardcoded override uses const args: any[] = []. This is consistent with the existing pattern used by all other generated methods (line 327), so it is not a new regression, but worth noting.

3. Incidental API_REFERENCE changes bundled in commit 3 -- The testDummyMethod -> close change and TradesParams description removal are side effects of re-running the API reference generator against the current BaseExchange.ts. These are legitimate but unrelated to the PR title. Not blocking.

4. Regression test reads source file from disk (core/test/pipeline/baozi-websocket-resolvers.test.ts:6-11) -- The test reads the websocket.ts file as a string and regex-matches against it. This is a pattern lint test, not a runtime test. It will correctly fail if someone reintroduces the ! pattern. Acceptable approach for this kind of guardrail.

PMXT Pipeline Check

• Field propagation (3-layer): N/A (no new unified type fields)
• OpenAPI sync: N/A (no BaseExchange.ts changes)
• Type safety: OK (no new any beyond existing generator pattern)

Semver Impact

minor (or arguably major due to finding #1) -- The PolymarketUS rename breaks the public Python API. If Polymarket_us was ever documented or used by consumers, this is a major change. If it was always considered a generator bug that shipped before anyone used it, minor is defensible.

Risk

• Tests were not run due to sandbox permission restrictions. The PR author's verification commands should be run before merge.
• The Polymarket_us -> PolymarketUS rename is a public API break for the Python SDK. Assess whether any users depend on the old name.