fix: align tooling config and docs with requires-python >=3.11

[emmcygn]

Summary

requires-python is set to >=3.11, but several tooling configs and documentation pages still reference Python 3.9 or 3.10. This PR brings
everything into alignment.

Tooling config (pyproject.toml)

Setting	Before	After
[tool.ruff] target-version	"py310"	"py311"
[tool.mypy] python_version	"3.10"	"3.11"
Trove classifier	includes Python :: 3.10	removed (not installable on 3.10)

Documentation — Python version references

• docs/installation.rst: conda example used python=3.10 and noted >=3.9 — updated to 3.11 and >=3.11
• docs/troubleshooting/installation.rst: conda example used python=3.9 — updated to 3.11

Documentation — broken links

Several pages linked to opensky_impala.html or opensky_usage.html, which no longer exist. Updated to point to data_sources/opensky_db.html:

• docs/gallery/heatmaps.rst
• docs/gallery/covid19.rst (also removed a dead external link to traffic-viz.github.io/opensky_impala.html)
• docs/paper/sectflow.rst
• docs/paper/atc_detect.rst

Verification

• ruff check passes with the new py311 target
• ruff format --check passes
• No code changes — config and docs only

[xoolive]

Thank you @emmcygn but honestly, I am working a big update/upgrade (probably leading to major traffic version) where these changes will become irrelevant.
I will leave the PR open until the new version is published but not merge yet (i am afraid it messes things up when I bring the changes to master)

[emmcygn]

Thanks, @xoolive excited to see it! Was just hoping to open a first PR as I'd love to contribute more over time to this project. Keen to learn about which areas would be especially appreciated to be supported with contributions.