Add Python 3.11, 3.12, 3.13 to CI test matrix

- Update GitHub Actions workflow to test Python 3.8-3.13
- Update CLAUDE.md to reflect expanded Python version support
- Remove obsolete six dependency reference from CLAUDE.md

Author: andrewleech

.github/workflows/python-package.yml

@@ -16,7 +16,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.8", "3.9", "3.10"]
+        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12", "3.13"]
 
     steps:
     - uses: actions/checkout@v3

CLAUDE.md

@@ -130,15 +130,14 @@ After tests complete, examine `debug.log` for full request/response traces.
 
 ### CI/CD
 GitHub Actions workflow (`.github/workflows/python-package.yml`) runs on push/PR to master:
-- Tests Python 3.8, 3.9, 3.10
+- Tests Python 3.8, 3.9, 3.10, 3.11, 3.12, 3.13
 - Builds package and validates with twine
 - Runs litmus test suite
 
 ## Version Management
 Uses `git-versioner` for version numbers from git tags. Version is read from `pywebdav.__version__` which is populated by the versioner.
 
 ## Dependencies
-- `six`: Python 2/3 compatibility (maintained for legacy reasons)
 - `git-versioner`: Version management from git tags
 
 Optional: