fix: suppress Python 3.14 deprecation warnings for asyncio policy API (#3129)

[r266-tech]

Description

Fixes #3129

Python 3.14 deprecates asyncio.get_event_loop_policy() and asyncio.set_event_loop_policy() with DeprecationWarning. These APIs are still the recommended way to configure uvloop and Windows event loop policies, so the fix wraps calls in warnings.catch_warnings() on Python >= 3.14 to suppress warnings originating from the asyncio module.

Changes

• sanic/server/loop.py: Wrapped event loop policy checks in warnings.catch_warnings() blocks for both try_use_uvloop() and try_windows_loop() functions

Testing

On Python 3.14, running Sanic with uvloop should no longer emit:

DeprecationWarning: 'asyncio.get_event_loop_policy' is deprecated and slated for removal in Python 3.16
DeprecationWarning: 'asyncio.set_event_loop_policy' is deprecated and slated for removal in Python 3.16

The pattern is intentionally kept simple — once Python 3.16 provides a loop_factory API, the warnings.catch_warnings wrapper can be replaced with direct set_event_loop_factory() calls.

[codecov]

Codecov Report

❌ Patch coverage is 41.66667% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.768%. Comparing base (785d77f) to head (759a319).

Files with missing lines	Patch %	Lines
sanic/server/loop.py	41.666%	6 Missing and 1 partial ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #3146       +/-   ##
=============================================
- Coverage   87.793%   87.768%   -0.025%     
=============================================
  Files          105       105               
  Lines         8143      8151        +8     
  Branches      1290      1292        +2     
=============================================
+ Hits          7149      7154        +5     
- Misses         687       690        +3     
  Partials       307       307               

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[themavik]

module=asyncio in warnings.filterwarnings hides every DeprecationWarning from asyncio inside try_use_uvloop and try_windows_loop, not only the policy call. nit: narrow with message= if tests still pass.