Replace utcnow() with timezone-aware object

[leewujung]

This PR addresses the warning
datetime.datetime.utcfromtimestamp() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.fromtimestamp(timestamp, datetime.UTC).
that occurs in various places in our codebase.

[leewujung]

Ugh @ctuguinay sorry this is not ready for review yet. I'll ping again once it is.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 72.72727% with 3 lines in your changes missing coverage. Please review.

Project coverage is 71.31%. Comparing base (9f56124) to head (a95065b).
Report is 203 commits behind head on main.

Files with missing lines	Patch %	Lines
echopype/consolidate/api.py	75.00%	1 Missing ⚠️
echopype/echodata/echodata.py	66.66%	1 Missing ⚠️
echopype/mask/api.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1484       +/-   ##
===========================================
- Coverage   83.52%   71.31%   -12.21%     
===========================================
  Files          64       22       -42     
  Lines        5686     1492     -4194     
===========================================
- Hits         4749     1064     -3685     
+ Misses        937      428      -509     

Flag	Coverage Δ
unittests	71.31% <72.72%> (-12.21%)	⬇️

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[leewujung]

Turns out that datetime.UTC was only added in python=3.11 so the 3.10 test is failing!

Onward with a version handler.

[leewujung]

@shivam096 : I haven’t had a chance to get back to this, but perhaps this would be a standalone issue that you can jump on easily? I haven’t looked at the latest failing report, but if the tests that are failing are actually not related to utcnow, let me know and we can see whether to address it in another PR or this one.

[leewujung]

This is superseded by #1497. Closing now.