fix: resolve cross-platform test failures on Windows and Ubuntu

- Add proper cross-platform path handling with Path.resolve()
- Fix file encoding issues by explicitly using UTF-8
- Correct mock paths to use google.generativeai instead of gemini_server.genai
- Create setup.py for proper package installation in CI
- Add conftest.py with Windows asyncio compatibility
- Update CI workflow to install package with pip install -e .
- Add import tests to verify package installation
- Set PYTHONPATH in test environment
- Simplify import mechanism in tests

These changes ensure tests pass consistently across Windows, Ubuntu, and macOS platforms.

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

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

.github/workflows/test.yml

@@ -25,14 +25,16 @@ jobs:
 
     - name: Install dependencies
       run: |
-        python -m pip install --upgrade pip
+        python -m pip install --upgrade pip setuptools wheel
+        pip install -e .
         pip install -r requirements.txt
 
     - name: Run tests with pytest
       env:
         GEMINI_API_KEY: "dummy-key-for-tests"
+        PYTHONPATH: ${{ github.workspace }}
       run: |
-        pytest tests/ -v --cov=gemini_server --cov-report=xml --cov-report=term
+        python -m pytest tests/ -v --cov=gemini_server --cov-report=xml --cov-report=term -x
 
     - name: Upload coverage to Codecov
       if: matrix.os == 'ubuntu-latest' && matrix.python-version == '3.11'
@@ -56,7 +58,7 @@ jobs:
     
     - name: Install dependencies
       run: |
-        python -m pip install --upgrade pip
+        python -m pip install --upgrade pip setuptools wheel
         pip install flake8 black isort mypy
         pip install -r requirements.txt