Unpin kerchunk (set floor) and enable Python 3.12

[jsignell]

Closes #77

Given that fsspec/kerchunk#445 seems to be resolved on main. This PR unpins the kerchunk version and uses the unreleased version newly released 0.2.5 instead. To me it seems fair that this library would sometimes require unreleased kerchunk and that feels preferable to pinning down to an old release.

[TomNicholas]

Thanks for spotting that kerchunk has fixed that bug @jsignell !

I'm hesitant to pin this package to kerchunk main because I would like the reliability of knowing we are pinning to a released version... If stuff like this can be fixed on kerchunk main without notice it could also get broken...

EDIT: Ideally kerchunk would release and then we pin to that.

[jsignell]

To be fair it was already fixed on main when the original ticket was opened. But yeah I see the hesitation. Let's ask for a kerchunk release :)

[jsignell]

fsspec/kerchunk#457

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.73%. Comparing base (f226093) to head (36dfb7b).
Report is 16 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #108      +/-   ##
==========================================
+ Coverage   90.18%   90.73%   +0.55%     
==========================================
  Files          14       18       +4     
  Lines         998     1144     +146     
==========================================
+ Hits          900     1038     +138     
- Misses         98      106       +8     

Flag	Coverage Δ
unittests	90.73% <ø> (+0.55%)	⬆️

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