#29053 adds tox.ini to support testing the sage distribution in isolated environments via docker.

This ticket adds toxenvs local-homebrew-macos-{minimal,standard} for testing with (best-effort) isolated installations of homebrew on macOS (not using docker).

To test:

    brew install tox
    tox -e local-homebrew-macos-standard

See comments in tox.ini for more examples.

An example run of that is here: https://github.com/mkoeppe/sage/actions/runs/32812271

Depends on #29335
Depends on #29361

CC: @dimpase @jhpalmieri @mwageringel @vbraun @tscrim

Component: porting

Author: Matthias Koeppe

Branch/Commit: dfce7d4

Reviewer: Dima Pasechnik, John Palmieri

Issue created by migration from https://trac.sagemath.org/ticket/29104