feat(test): Upgrade pytest to version 9.x

Upgraded pytest from <8.5 to <9.1 to adopt the latest testing framework
features and improvements.

Changes:
- Updated pytest requirement from <8.5 to <9.1
- Updated pytest-asyncio to >=1.3.0 for pytest 9 compatibility

Testing:
- All 31 tests pass successfully
- No pytest-specific deprecation warnings detected
- Verified compatibility with existing test suite including:
  - Tornado AsyncHTTPTestCase tests
  - pytest-asyncio async tests
  - pytest fixtures

The upgrade is safe and backward-compatible with our current test patterns.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: Tim020

server/test_requirements.txt

@@ -1,5 +1,5 @@
-pytest<8.5
-pytest-asyncio
+pytest<9.1
+pytest-asyncio>=1.3.0
 pylint==3.3.9
 black==25.11.0
 isort==5.13.2