Implement async HTTP client wrapper using httpx

[codebestia]

Description

An async counterpart to the sync client using httpx.AsyncClient, enabling use in async frameworks like FastAPI, Starlette, and Django async views. It should share the same configuration and interface as the sync client so resource methods can delegate to either with minimal branching.

Proposed Steps

• Add _AsyncHTTPClient to http_client.py, mirroring the sync interface with async def request(...).
• Accept the same constructor arguments as _SyncHTTPClient.
• Use async with httpx.AsyncClient(...) as client lifecycle management.
• Extract a shared _build_request(method, path, params, json) helper used by both sync and async versions.

Acceptance Criteria

• await client.request("GET", "/payments") returns the same response shape as the sync version.
• The async client can be used in a pytest-asyncio test without event loop conflicts.
• Closing the async client (via aclose()) is properly awaited.
• Sync and async clients share URL-building and header logic without duplication.

[fathiaoyinloye]

I'd like to work on this issue.

I have experience building API clients, asynchronous applications, and automated testing. After reviewing the requirements, I understand that the goal is to introduce an asynchronous client implementation that mirrors the existing synchronous interface while sharing as much request-building logic as possible.

My approach would be to:

• Implement an async HTTP client that matches the behavior and interface of the existing sync client.
• Extract shared request construction logic to avoid duplication between sync and async implementations.
• Ensure consistent URL building, header handling, and response shapes across both clients.
• Add proper async lifecycle management, including support for clean client shutdown.
• Add test coverage for async usage scenarios and verify compatibility with async test environments.
• Ensure the implementation remains backward compatible with existing consumers.

I'll make sure the solution is well-tested, maintainable, and aligned with the project's existing architecture.

Please assign this issue to me if it is available. Thank you!

[grantfox-oss]

🦊 GrantFox — @fathiaoyinloye has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #8)
2. Your PR will be reviewed by the ShadeProtocol maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🦊 GrantFox — @fathiaoyinloye has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #8)
2. Your PR will be reviewed by the ShadeProtocol maintainers

Good luck! Track your progress on GrantFox.