Add AsyncRetryingContext class (A)

[heri16]

This implementation uses a single shared async context manager.
See Issue #48

Example:

async with AsyncRetryingContext(open, wait=wait_fixed(2))('filename.txt', 'r') as file:
  ...

Flow: AsyncContextManager(func, retry_opts)(func_args) -> async_retriable_func(func_args) -> [func_result] -> file

Outputs an async context manager that generates async_retriable_func on __aenter__. It then internally passes in func_args into this async_retriable_func and awaits for the func_result.

• If the func_result is a value, this value is returned by by __aenter__ to be passed into the new context as file.
• If the func_result is another context manager, it also calls __enter__ on this wrapped context manager. If __enter__ returns a truthy value, this value is in turn returned by __aenter__ to be passed into the new context as file.

[heri16]

Ok, this implementation has no merit. Closing.