[Work Item] Implement get_datastreams() method

[Sam-Bolling]

📌 Task Description

Implement the getDatastreams(params: Record<string, string>) method in src/client/connectedSystemsClient.ts. This method should retrieve datastream metadata from CSAPI-compliant servers using flexible query parameters.

This method is part of the extended CSAPI support and should follow the same modular, compositional design as core methods. It will be exposed via .connectedSystems only if CSAPI capability is detected.

✅ Acceptance Criteria

• Method getDatastreams(params: Record<string, string>) created
• Returns parsed response from CSAPI /datastreams endpoint
• Integrated into ConnectedSystemsClient class
• Covered by unit tests using vitest or jest
• Includes JSDoc comments for documentation
• Linked to GitHub Project board

🔗 Related Links

• Implementation Plan
• Upstream Issue #118