Drop Python 3.9 support #1

Context

The workspace is retiring Python 3.9 support. GitHub Actions ubuntu-latest is moving to Ubuntu 26.04, for which actions/setup-python does not provide CPython 3.9 builds. CPython 3.10 builds are available.

Scope

Raise the minimum and Ruff target to Python 3.10 and replace the 3.9 CI boundary; update active API/development/interoperability documentation and next-release notes. Preserve standalone operation, optional HDF5/registry extras, clean-environment CLI and Python 3.12 Pyodide coverage.

Delivery and acceptance

• Target branch: develop.
• One dedicated PR for this repository, linked to this issue; preserve unrelated changes and published historical artifacts.
• Validate changed behavior and metadata on the retained runtimes; report exact results and unavailable checks.
• Keep ubuntu-latest; do not globally upgrade dependency bounds or add Python 3.15 support.
• Merge only after applicable checks pass on the current PR head and branch protections are satisfied. Where no PR CI exists (Camera, Pulse and platform docs), documented local validation is the explicitly approved gate.
• Close this issue only after the corresponding PR is verified as merged. No package release or promotion to another stable branch is authorized by this task.