Implement pagination helper utilities for list endpoints in @astroid/client

[Cjay-Cyber-2]

Description — what to implement and the why/impact.

Listing resources such as agents, transactions, and budgets returns paginated datasets from the backend API. Developers and agents need ergonomic pagination helpers and async iterators to seamlessly consume multi-page results without manual cursor management.

Context & Requirements — background, constraints, design references, edge cases; grounded in the actual repo (real files, stack, conventions).

Provide helper utilities or async generators in @astroid/client that accept a list query function and iterate through cursors (cursor, limit, has_more) automatically, yielding individual items or pages as requested.

Acceptance Criteria — a checklist ("- [ ] ...") of specific, testable conditions that define "done".

• Implement an async generator function for paginating resource lists.
• Support standard cursor-based pagination parameters (cursor, limit).
• Handle empty result sets and termination conditions correctly.
• Add comprehensive unit tests mocking paginated API responses.

Implementation Guidance — likely files/modules to touch (use real paths from the repo context) and a suggested approach, without over-prescribing.

Check packages/client/src/ for existing query builders or response interfaces. Design the helper to be generic over item types and response DTOs.

Testing & Validation — how the contributor should prove it works (tests to add/run, manual checks, screenshots for UI).

Run pnpm test --filter @astroid/client and ensure all tests pass.

Submission Guidelines — must open a PR that includes "Closes #"; assignment is required before starting; follow the repo's existing style and conventions.

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Wave complexity: Medium