feat(sdks): forward SuiBets exchange api base URL credential

[Bortlesboat]

Why

Closes #1388. The core exchange factory reads credentials?.baseUrl as the SuiBets exchange's own API origin (core/src/server/exchange-factory.ts), falling back to SUIBETS_BASE_URL. Neither SDK could forward that value: SDK-level baseUrl / base_url means the PMXT sidecar URL, a different concept, and is never included in the credentials payload. Follow-up to #1657, which closed the same gap for walletAddress.

What

Both SDKs gain an option that forwards into the credentials payload as baseUrl, named to avoid colliding with the sidecar URL option:

• TypeScript: SuiBetsOptions.apiBaseUrl — stored on the client, merged into getCredentials() output as baseUrl when set.
• Python: SuiBets(api_base_url=...) + SuiBetsOptions.api_base_url — same forwarding in _get_credentials_dict().

When unset, behaviour is unchanged (sidecar falls back to SUIBETS_BASE_URL).

Testing

• Python: pytest tests/ — 267 passed (the 2 test_server_manager errors are a pre-existing Windows temp-dir permission issue, present on clean main). New tests cover forwarding alongside wallet_address and alone.
• TypeScript: npx jest tests/exchange-credentials.test.ts — 3 passed; tsc --noEmit clean. New tests mirror the Python cases.