TST: improving reliability of `oldestdeps` ?

hey @pllim, I noticed you had to manuallyfix `oldestdeps` in 2fb9a779f9a7c1e7cc8b2470d495793ef8828072 which, as I gathered, served as a patch against a stealth upgrade (`pyparsing` being a transitive dep, it's never pinned). We could instead apply the same solution I used in `astropy`, using `uv` (+ `tox-uv` to avoid ditching `tox`) to re-define `oldestdeps` as synonymous with a resolution strategy (`lowest`), so this failure mode is obliterated once and for all. I understand this repo is under-maintained, which I think is all the more reason to make its CI as stable as we can. What do you think ?

Start by inspecting the repository’s tox/CI configuration and the `oldestdeps` definition, then review commit `2fb9a779f9a7c1e7cc8b2470d495793ef8828072` to understand the manual fix for the transitive `pyparsing` upgrade. Compare the current failure behavior with the proposed `uv` and `tox-uv` approach; done means the oldest-dependency CI job reliably uses the lowest resolution strategy and passes.

Written by the indexing model from the issue text.