Require typing_extensions with Self support on Python 3.10

[Doribelove]

Summary

On Python 3.10, spatialmath.base._types_39 imports Self from typing_extensions. The current unbounded dependency allows typing_extensions==3.10.0.2, which lacks Self and makes import spatialmath fail. Require typing_extensions>=4.0.0, the first release with Self, so the package metadata reflects this import requirement.

Validation

• With typing_extensions==3.10.0.2, reproduced ImportError: cannot import name 'Self' from 'typing_extensions' before the metadata change.
• Reinstalled the editable package after the change; dependency resolution upgraded typing_extensions to 4.16.0 and import spatialmath succeeded.
• Also checked that import spatialmath succeeds with the minimum allowed version, 4.0.0.
• With the resolved current dependency set, pytest -q --disable-warnings: 347 passed, 3 skipped (Python 3.10.12); git diff --check passed.

Fixes #78. Prepared and validated with OpenAI Codex assistance.

[petercorke]

Thank you for tracking this down — #78 has been open since May 2023 with the root cause already correctly diagnosed in the comments, but nobody ever followed through with a fix. Nice to see it closed out.

I reproduced it independently before approving: a genuinely isolated Python 3.10 venv, typing_extensions==3.10.0.2 forced in last (so nothing else silently re-resolved it), gives exactly the ImportError: cannot import name 'Self' from #78. With this change, both reinstalling into that same venv and a completely fresh pip install -e . resolve typing_extensions to 4.16.0 and import cleanly.

For reference, this doesn't overlap with #212 (which collapses the per-Python-version type shim into one file) — that PR keeps the same unconditional typing_extensions import on 3.10 and doesn't touch this dependency pin, so the two are complementary rather than conflicting.

Approving — thanks for the fix.