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[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

Additional details and impacted files

```diff @@ 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](https://app.codecov.io/gh/HERA-Team/hera_pspec/pull/397/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=HERA-Team) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/HERA-Team/hera_pspec/pull/397/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=HERA-Team) | `96.17% <100.00%> (+0.17%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=HERA-Team#carryforward-flags-in-the-pull-request-comment) to find out more.

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