fix: omit user stream market filter for all markets

[cesarenaldi]

Summary

• Omit the user stream markets filter when subscribing to all markets
• Keep narrowed user stream subscriptions sending markets: [...]
• Add coverage for the broad user stream initial subscribe frame

Verification

• pnpm lint
• pnpm typecheck
• pnpm test:client

Notes

• This matches the Python SDK fix in fix: omit user stream market filter for all markets py-sdk#103.

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Note

Low Risk
Small protocol-shape change for user WebSocket subscribe frames; narrowed subscriptions are unchanged and coverage was added.

Overview
Fixes the initial CLOB user WebSocket subscribe frame so a broad subscription no longer sends a markets field.

buildUserSubscribeMessage still always includes auth and type: 'user', but it only adds markets when includeAllMarkets is false. Narrow subscriptions keep sending markets: [...]; all-markets subscriptions match the server expectation of an unfiltered stream (same behavior as the Python SDK fix).

Adds a test that subscribing with { topic: 'user' } alone produces a frame with auth and type only.

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