fix: Python 3.14 compatibility for deprecated asyncio APIs

[daniel7an]

Summary

Fixes #3132

Python 3.14 deprecated several asyncio APIs that Sanic uses, causing DeprecationWarnings (which become errors with -W error) and, in some code paths, RuntimeErrors due to asyncio.get_event_loop() no longer creating an implicit event loop.

Changes

sanic/server/loop.py

• Wrap asyncio.get_event_loop_policy() and asyncio.set_event_loop_policy() calls in warnings.catch_warnings() to suppress the deprecation warnings (deprecated in 3.14, removal in 3.16). This also suppresses the cascading asyncio.AbstractEventLoopPolicy deprecation from uvloop.

sanic/mixins/startup.py

• Replace get_event_loop() with get_running_loop() in create_server() (async method) and stop() — both run inside an event loop, so get_running_loop() is correct and doesn't trigger the Python 3.14 deprecation/error.

sanic/app.py

• Suppress deprecation warning in the loop property fallback path that uses get_event_loop_policy().get_event_loop().

sanic/server/runners.py

• Suppress uvloop's internal use of deprecated asyncio.iscoroutinefunction in loop.add_signal_handler() calls.

sanic/server/websockets/impl.py

• Replace asyncio.get_event_loop() with asyncio.get_running_loop() — this code always runs within an active event loop.

Testing

• All signal-related tests pass (test_signals.py, test_signal_handlers.py)
• Production mode (single and multi-worker) starts and serves requests without deprecation warnings on Python 3.14.2
• Verified with python3 -W error::DeprecationWarning — no sanic-originated deprecation warnings remain.

[codecov]

Codecov Report

❌ Patch coverage is 54.54545% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.800%. Comparing base (785d77f) to head (67108d3).

Files with missing lines	Patch %	Lines
sanic/server/loop.py	55.555%	4 Missing ⚠️
sanic/server/websockets/impl.py	0.000%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #3139       +/-   ##
=============================================
+ Coverage   87.793%   87.800%   +0.007%     
=============================================
  Files          105       105               
  Lines         8143      8148        +5     
  Branches      1290      1290               
=============================================
+ Hits          7149      7154        +5     
- Misses         687       688        +1     
+ Partials       307       306        -1     

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[Tronic]

Suppression of deprecation warnings is not the right solution. Python 3.16 comes very soon.