test: add unit tests for @voltagent/resumable-streams

[nuthalapativarun]

Problem

The @voltagent/resumable-streams package (v2.0.2) has zero test coverage. No .spec.ts files exist despite vitest being configured.

Proposed Solution

Add unit tests covering:

• resumable-streams.ts — factory functions, store type markers, disabled-state detection
• chat-session.ts — createResumableChatSession create/resume/complete flows

Using mocks for Redis and VoltOps dependencies.