Getting our dependencies sensibly versioned

[pc494]

Currently we are very permissive with our dependencies, I would like (in anticipation of 1.0.0) to tighten them up a bit, broadly aiming for the latest minor version. For now I'm not particularly concerned with docs code. Using tests as an example:

    "tests": [
        "pytest     >= 8.0", # up from 5
        "pytest-cov >= 4.0", # up from 2
        "pytest-xdist" >= 3.0, # up from unforced
        "pytest-rerunfailures >13.0", #up from unforced 
        "coveralls  >= 3.0", #up from 1
        "coverage   >= 7.0", #up from 5
    ],

This helps avoid people writing in (sort of) niche bugs (e.g. nose-style testing which was allowed in pytest prior to 8.0). This would tie in with a cron-job to make for a more consistent experience.