fix: bad dtype definition for dak.num(..., axis=0) metadata

[douglasdavis]

np.int64 is not a proper dtype, np.dtype("int64") is.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (fa07194) 93.94% compared to head (a1b55a2) 93.94%.

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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #417   +/-   ##
=======================================
  Coverage   93.94%   93.94%           
=======================================
  Files          23       23           
  Lines        3123     3123           
=======================================
  Hits         2934     2934           
  Misses        189      189           

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[ikrommyd]

It works for me but I'm getting a warning

In [9]: dak.num(events, axis=0).compute()
/Users/iason/fun/coffea_dev/dask-awkward/src/dask_awkward/lib/optimize.py:150: UserWarning: The necessary columns optimization failed; exception raised:

<class 'AssertionError'> with message bug in Awkward Array: attempt to convert TypeTracerArray into a concrete array.

Please see the FAQ section of the docs for more information:
https://dask-awkward.readthedocs.io/en/stable/more/faq.html

Is this fine?

[douglasdavis]

Nope! fixed the warning :)