[BUG] fix deep_equals for np.array with dtype="object"

[fkiraly]

This PR fixes an unreported bug where deep_equals would break on np.array with dtype="object", this is due to the equal_nan=True setting in np.array_equal which will lead to an exception if dtype="object"`.

Also includes test cases covering this.

Mirror of sktime/sktime#5697 (duplicated prior to ongoing refactor)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3bb51d8) 84.65% compared to head (a5a3846) 84.69%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #263      +/-   ##
==========================================
+ Coverage   84.65%   84.69%   +0.04%     
==========================================
  Files          43       43              
  Lines        2926     2928       +2     
==========================================
+ Hits         2477     2480       +3     
+ Misses        449      448       -1     

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