fix(sdk): expose venue filters in fetch params

[realfishsam]

Summary

• Adds sourceExchange / exchange venue filter aliases to TypeScript market/event fetch parameter interfaces.
• Adds matching source_exchange / exchange TypedDict keys to Python market/event fetch parameter types.

Fixes #1317
Fixes #1318

Test Plan

• python3 -m py_compile sdks/python/pmxt/models.py
• git diff --check

Note: TypeScript compiler validation was attempted, but this cron host could not install workspace dependencies because npm install failed with ENOSPC: no space left on device. The change is type-only and mirrors the already-present core BaseExchange fetch parameter fields.

[realfishsam]

PR Review: PASS (NOT VERIFIED)

What This Does

Adds venue-filter aliases to SDK fetch parameter types: sourceExchange / exchange for TypeScript and source_exchange / exchange for Python. This improves SDK consumer type hints for filters the sidecar/core already accept at runtime.

Blast Radius

Type-only SDK surface in sdks/typescript/pmxt/models.ts and sdks/python/pmxt/models.py. No core exchange normalizers, OpenAPI schema, sidecar routes, generated clients, or SDK transport/conversion shims are changed.

Consumer Verification

Before (base branch):
The runtime clients already forward arbitrary params to the sidecar, but the typed SDK parameter models did not advertise venue filters. TypeScript MarketFilterParams / EventFetchParams and Python MarketFetchParams / EventFetchParams lacked these keys, so typed consumers could see static type errors when passing venue filters.

// before: no sourceExchange/exchange properties in MarketFilterParams/EventFetchParams
await client.fetchMarkets({ sourceExchange: 'polymarket' }); // runtime-forwardable, not typed

After (PR branch):
The TypeScript and Python type surfaces now include the aliases:

// sdks/typescript/pmxt/models.ts:453-457, 506-510
sourceExchange?: string;
exchange?: string;

# sdks/python/pmxt/models.py:749-750, 769-770
source_exchange: str
exchange: str

This is not directly observable through the HTTP consumer path because the PR only changes static type definitions; the existing SDK transport already serializes supplied params.

Test Results

• Build: NOT VERIFIED (full TypeScript SDK compile is blocked in this checkout by missing generated artifacts: Cannot find module '../generated/src/index.js' from pmxt/client.ts and pmxt/server-manager.ts)
• Unit tests: PASS for Python syntax (python3 -m py_compile sdks/python/pmxt/models.py)
• Server starts: N/A (type-only SDK change)
• E2E smoke: N/A (no runtime behavior changed)
• Focused TypeScript type syntax: PASS (npx tsc --noEmit --skipLibCheck --moduleResolution node --target ES2020 --module commonjs sdks/typescript/pmxt/models.ts)

Findings

No blocking findings.

PMXT Pipeline Check

• Field propagation (3-layer): N/A — no unified response fields added.
• OpenAPI sync: N/A — no sidecar API shape changed.
• Financial precision: N/A
• Type safety: OK for the changed model file; full SDK compile was not verified because generated SDK artifacts are absent in this review environment.
• Auth safety: N/A

Semver Impact

patch -- type-surface fix for existing/forwarded fetch params, with no runtime API break.

Risk

Generated SDK artifacts are unavailable in this checkout, so I could not run the full TypeScript SDK compile. Since the PR only widens parameter types, the remaining risk is limited to publication/type-generation parity rather than runtime behavior.