Drop Python 3.8 support and consolidate lint workflow

[jupe]

Summary

• require Python 3.9+ in package metadata and drop the 3.8 classifier
• fold the standalone pylint workflow into the primary test workflow and remove the old file
• update the CI test matrix to cover Python 3.9-3.12 only

Testing

• ⚠️ python -m pip install -e .[dev] (fails: proxy blocks access to PyPI)
• ⚠️ pytest (fails: missing optional dependency appium without network access to install)

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https://chatgpt.com/codex/tasks/task_b_68d2e0cbee948333a9a9bf2310de080c