[BUG] Python 3.14 compatibility: use inspect.iscoroutinefunction instead of asyncio.iscoroutinefunction

[Binilkks]

Describe the bug
The codebase uses asyncio.iscoroutinefunction, which is deprecated in Python 3.14.
This causes deprecation warnings and may break in future Python versions.

To Reproduce
Steps to reproduce the behavior:
Run the code or tests with Python 3.14.
Observe deprecation warnings for asyncio.iscoroutinefunction

Expected behavior
The code should use inspect.iscoroutinefunction for compatibility with Python 3.14 and later.

Screenshots
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Environment:

• OS: macOS
• FastAPI Utils version : 0.8.0

import fastapi_utils
import fastapi
import pydantic.utils
print(fastapi_utils.__version__)
print(fastapi.__version__)
print(pydantic.utils.version_info())

• Python version, get it with:

python --version

Additional context
Add any other context about the problem here.