new feature: Async support for C binding

### Feature Description

[OceanBase](https://github.com/oceanbase/oceanbase) currently utilizes libaio to implement async r/w operations for the file system. We hope that OpenDAL C bindings can provide a similar mechanism to enable async r/w operations for object storage.

### Problem and Solution

similar feature: [Tracking Issue: Async support for C++ binding](https://github.com/apache/opendal/issues/5194)

### Additional Context

_No response_

### Are you willing to contribute to the development of this feature?

- [X] Yes, I am willing to contribute to the development of this feature.

The issue names OpenDAL's C bindings and the linked C++ async-support tracking issue, but no files, tests, or entry points. Start by locating the existing C binding API and reviewing issue #5194 for related scope. Done means defining and implementing an async read/write mechanism for object storage in the C bindings.

Written by the indexing model from the issue text.