Merge https://github.com/google/adk-python/pull/6107
## Summary
- Fix README claiming Python 3.11+ while the package requires `>=3.10`; sync all docs (README, AGENTS.md, adk-setup skill, two sample READMEs) to 3.10+
- Swap the rate-limited shields.io PyPI downloads badge for a pepy.tech one (the old badge rendered "rate limited by upstream service")
- Add a Python Unit Tests CI status badge
## Test plan
- [ ] Confirm README badges render correctly on GitHub (downloads + unit test status)
- [ ] Verify Python version wording matches `requires-python = ">=3.10"` in pyproject.toml
Co-authored-by: Wei Sun (Jack) <weisun@google.com>
COPYBARA_INTEGRATE_REVIEW=https://github.com/google/adk-python/pull/6107 from google:docs/readme-badges-python-310 bdfa1c125375abe94c343389702994cbc8857e7d
PiperOrigin-RevId: 931539712
Wei (Jack) Sun
d3c21d716e