add document for experimental async programming support

[Guest0x0]

some example code requires JS FFI, so I tweak the CI workflow and only check for JS backend for those examples

[peter-jerry-ye-code-review]

‼️ This code review is generated by a bot. Please verify the content before trusting it.

Here are three potential issues or observations from the provided git diff output:

1. Inconsistent Error Handling in Async Functions:

   • In the async_worker function, the suspend!! call is used with a callback that handles both normal resumption (resume_ok) and error resumption (resume_err). However, the error handling in the test block does not account for all possible errors. Specifically, the catch block in the test block only handles MyError, but the suspend!! call could potentially throw other types of errors. This could lead to unhandled exceptions in production code.

2. Potential Issue with return in PowerShell Script:

   • In the PowerShell script section, the return statement is used to skip processing the async directory if the backend is not js. However, return in PowerShell exits the entire script block, which might not be the intended behavior. If the intention is to skip only the current iteration of the loop, continue should be used instead of return.

3. Hardcoded Paths in Documentation:

   • The documentation includes hardcoded paths like next/sources/async/src/async.mbt. This could be problematic if the directory structure changes in the future. It might be better to use relative paths or a more flexible way to reference these files to avoid breaking the documentation when the project structure evolves.

These issues should be reviewed and addressed to ensure the robustness and maintainability of the code and documentation.