[TexasCoding]

Reconciles nightly spec drift (Spec Drift run 40320006492). Release 22.4.0 (minor).

Closes #556
Closes #557

Changes

• scripts/sync_spec.py + scripts/generate.py (re-vendored specs/openapi.yaml, specs/asyncapi.yaml, specs/perps_openapi.yaml; no hand edits in kalshi/_generated).
• CreateRFQBatchChild: optional contracts (contracts_fp, FixedPointCount) and target_cost (target_cost_dollars, DollarDecimal) with serialization_alias + AliasChoices, matching CreateRFQBatchRequest.
• Perps MarginMarket.halt_sources: list[str] | None = None. Spec marks it required; kept optional (PERPS_EXCLUSIONS entry, kind server_omits_despite_required) so this stays non-breaking.
• AsyncAPI 16 → 15 channels: core batch_communications removed; RFQ-batch messages now arrive on communications. The SDK never exposed a helper/model for it, so nothing was removed; notes added on subscribe_communications(), CommunicationsMessage, docs/websockets.md.
• Regression tests, docs, CHANGELOG, version 22.4.0.

Blast radius (manual; GitNexus unavailable)

• CreateRFQBatchChild: new optional fields default None and are excluded when unset → existing rfq_batches.create() payloads serialize identically. Used only by communications.rfq_batches.create (sync + async).
• MarginMarket: new optional field; existing constructors/fixtures and payloads without it still validate. Consumers: perps markets.list/get and anything embedding MarginMarket.
• WS: docstring-only changes; no routing/model change.
• Contract map / test exclusions: one new perps exclusion.

Gates

• uv run ruff check . ✅
• uv run mypy kalshi/ ✅
• uv run pytest tests/ --ignore=tests/integration -q ✅ 4935 passed, 3 skipped
• uv run pytest tests/test_contracts.py -W error::UserWarning ✅ 902 passed