test: enhance test framework with comprehensive fixtures and mocks

- Add shared mock builders for aiocqhttp, discord, telegram
- Add test helpers for platform configs and mock objects
- Expand conftest.py with test profile support
- Update coverage test workflow configuration

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: whatevertogo

.github/workflows/coverage_test.yml

@@ -37,7 +37,7 @@ jobs:
           mkdir -p data/temp
           export TESTING=true
           export ZHIPU_API_KEY=${{ secrets.OPENAI_API_KEY }}
-          pytest --cov=. -v -o log_cli=true -o log_level=DEBUG
+          pytest --cov=astrbot -v -o log_cli=true -o log_level=DEBUG
 
       - name: Upload results to Codecov
         uses: codecov/codecov-action@v5