fix: update Python version requirement to 3.10+

BREAKING CHANGE: Python 3.8 and 3.9 are no longer supported

- MCP package requires Python >=3.10 (all versions from 0.9.1 to 1.9.3)
- Update setup.py to require Python >=3.10
- Update GitHub Actions to only test Python 3.10, 3.11, and 3.12
- Update README.md with correct Python version requirement
- Remove typing-extensions dependency (not needed for Python 3.10+)
- Remove Python 3.8/3.9 from classifiers

This resolves all GitHub Actions failures for Python 3.8/3.9 tests.

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

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

.github/workflows/test.yml

@@ -13,7 +13,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        python-version: ['3.8', '3.9', '3.10', '3.11', '3.12']
+        python-version: ['3.10', '3.11', '3.12']
 
     steps:
     - uses: actions/checkout@v4