Use inspect.iscoroutinefunction instead of asyncio.iscoroutinefunction to avoid Python 3.14 deprecation warning

[edgarrmondragon]

The function asyncio.iscoroutinefunction was recently deprecated in Python 3.14.0a1 and will be removed in Python 3.16: https://docs.python.org/3.14/whatsnew/3.14.html#deprecated.

The function's had a consistent implementation at least since Python 3.7:

• https://github.com/python/cpython/blob/3.7/Lib/asyncio/coroutines.py#L160-L163
• https://github.com/python/cpython/blob/3.8/Lib/asyncio/coroutines.py#L164-L167
• https://github.com/python/cpython/blob/v3.9.20/Lib/asyncio/coroutines.py#L164-L167
• https://github.com/python/cpython/blob/v3.10.15/Lib/asyncio/coroutines.py#L164-L167
• https://github.com/python/cpython/blob/v3.11.10/Lib/asyncio/coroutines.py#L21-L24
• https://github.com/python/cpython/blob/v3.12.7/Lib/asyncio/coroutines.py#L20-L23

Which means it's safe to use inspect.iscoroutinefunction in this package without checking the Python version.

FWIW the deprecation first appears in:

https://github.com/python/cpython/blob/v3.14.0b1/Lib/asyncio/coroutines.py#L20-L27