Harmonize label format and tick resolution choosing logic

[spencerkclark]

🚀 Pull Request

This takes a fairly simple approach to addressing #48. Here I define a mapping between the resolution chosen by the tick locator depending on the range and number of ticks requested, and the date format for the labels on the axis.

The plot @klindsay28's example now produces is shown below:

[codecov-commenter]

Codecov Report

Merging #79 (63c53f7) into main (f42e64a) will increase coverage by 1.38%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##             main      #79      +/-   ##
==========================================
+ Coverage   89.20%   90.58%   +1.38%     
==========================================
  Files           1        1              
  Lines         176      170       -6     
  Branches       43       41       -2     
==========================================
- Hits          157      154       -3     
+ Misses         13       11       -2     
+ Partials        6        5       -1     

Impacted Files	Coverage Δでるた
nc_time_axis/__init__.py	90.58% <80.00%> (+1.38%)	⬆️

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[aulemahal]

This looks good, and more coherent! I see the potential issue with using a maybe-unset attribute from the other class, but let's leave that for another PR, when the issue comes up!

[spencerkclark]

Thanks @aulemahal -- in it goes!