Import iscoroutinefunction() from the inspect module on Python >= 3.14

[Hellzed]

From Python 3.14 on, importing iscoroutinefunction() from the asyncio module is deprecated, and will generate a warning. This function will be removed in Python 3.16.
https://docs.python.org/3/deprecations/index.html#pending-removal-in-python-3-16

This conditionally imports iscoroutinefunction() from the inspect module on Python 3.14 and above, so the project can now safely advertise compatibility with Python 3.14 (and earlier) versions.

Additionally, I've updated the test and release workflows for Python 3.14, is this okay?

[coveralls]

coverage: 92.683% (+0.2%) from 92.5%
when pulling 582dff5 on Hellzed:master
into ffad8a1 on syrusakbary:master.

[markedwards]

Thanks for the change. Might also be worth considering dropping 3.8 and 3.9 from coverage, since they are EOL. But I'm not sure it needs to be a goal to cut them off, so will leave it alone for now.

Will plan to do a 0.4.3 release in the coming days.