Speed up Table.__repr__ and potentially other forms of data access

[astrofrog]

This speeds up the Table.__repr__ by avoiding repeated calls to CasaArrayWrapper.__getitem__ with the same arguments (which is not actually cached by dask, see dask/dask#8420). For the particular example I was trying this speeds things up from 20 seconds to 5 seconds. To speed this up further, I will need to try and profile the dask data access in detail, but at least this was a low hanging fruit improvement, and 5 seconds is not too bad considering the size of the tables we are accessing.

This goes towards addressing #36

[codecov-commenter]

Codecov Report

Merging #38 (c5a5739) into main (95403b8) will decrease coverage by 0.05%.
The diff coverage is 22.22%.

❗ Current head c5a5739 differs from pull request most recent head b7112db. Consider uploading reports for the commit b7112db to get more accurate results

@@            Coverage Diff             @@
##             main      #38      +/-   ##
==========================================
- Coverage   44.94%   44.89%   -0.06%     
==========================================
  Files          17       17              
  Lines        2118     2125       +7     
==========================================
+ Hits          952      954       +2     
- Misses       1166     1171       +5     

Impacted Files	Coverage Δ
casa_formats_io/casa_dask.py	22.30% <22.22%> (+0.35%)	⬆️

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[astrofrog]

Since this is reasonably straightforward and to make it easier to try out, I'll go ahead and merge.