Tracking issues of Swift binding

#2470 introduced the Swift binding to OpenDAL. This issue is for tracking the remaining tasks of it.

## Tasks

- [x] Add contributing docs #2540
- [x] Refine package structure #2479
- [x] Add tests and CI actions #2492
- [ ] Complete the binding APIs
- [ ] Add release build for C library
- [ ] Add async supports

Review the unchecked tasks in this tracking issue, starting with completing the binding APIs, adding a C-library release build, and adding async support. Use the completed items and linked issues #2540, #2479, and #2492 for project context. Done means each remaining task is implemented and checked off with the relevant build or test coverage.

Written by the indexing model from the issue text.