Added tests re. future array shapes and ensured compatibility in utils

[adeliegorce]

Following @JianrongTan's issue #396 , this PR

1. Fixes a backward compatibility issue in utils.uvd_to_Tsys which raised an error when the UVData file used has future_array_shapes=False
2. Adds tests to test_utils to ensure backwards compatibility of the code with and without future array shapes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.17%. Comparing base (a5f458f) to head (01857a8).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #397      +/-   ##
==========================================
+ Coverage   95.99%   96.17%   +0.17%     
==========================================
  Files          17       17              
  Lines        6118     6118              
==========================================
+ Hits         5873     5884      +11     
+ Misses        245      234      -11     

Flag	Coverage Δ
unittests	96.17% <100.00%> (+0.17%)	⬆️

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[JianrongTan]

Looks all good to me. Thanks @adeliegorce!