Minor deprecation fixes

[sdhiscocks]

• Fix deprecated array wrap method without context/return_scalar
• Fix deprecated utcfromtimestamp
• Fix deprecation warnings for ndim > 0 arrays becoming scalar
• Fix deprecated utcnow

[codecov]

Codecov Report

Attention: Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review.

Project coverage is 93.93%. Comparing base (f67aead) to head (608446f).

Files	Patch %	Lines
stonesoup/reader/opensky.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1045      +/-   ##
==========================================
+ Coverage   93.90%   93.93%   +0.02%     
==========================================
  Files         204      204              
  Lines       13345    13345              
  Branches     2730     2730              
==========================================
+ Hits        12532    12536       +4     
+ Misses        551      549       -2     
+ Partials      262      260       -2     

Flag	Coverage Δ
integration	67.26% <42.10%> (+0.02%)	⬆️
unittests	88.58% <89.47%> (+0.02%)	⬆️

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[sdhiscocks]

stonesoup/reader/opensky.py 0.00% 2 Missing ⚠️

Tested locally (--remote-data flag set) and passing.