[FIX] Feature Statistics: Error in time variable display

[ales-erjavec]

Issue

Feature Statistics raises error when displaying time variable with a formatted representation.

  File "/Users/aleserjavec/workspace/orange3/Orange/widgets/data/owfeaturestatistics.py", line 575, in data
    return roles[role]()
  File "/Users/aleserjavec/workspace/orange3/Orange/widgets/data/owfeaturestatistics.py", line 540, in display
    return render_value(self._center[row])
  File "/Users/aleserjavec/workspace/orange3/Orange/widgets/data/owfeaturestatistics.py", line 518, in render_value
    str_val = format_zeros(str_val)
  File "/Users/aleserjavec/workspace/orange3/Orange/widgets/data/owfeaturestatistics.py", line 505, in format_zeros
    if float(str_val) == 0:
ValueError: could not convert string to float: '2001-12-31 18:12:00'

The error however might not on show up on macOS in ErrorReporting dialog.

This is probably the reason behind issue gh-5009.

Description of changes

• Fix error in formatting
• Optimize attribute/class_vars/meta membership tests in the model. Was slow O(n_variables) before (noticeable on n_variables > 500)

Includes

• Code changes
• Tests
• Documentation

[codecov]

Codecov Report

Merging #5152 (7b0b946) into master (e2eb828) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #5152   +/-   ##
=======================================
  Coverage   84.77%   84.78%           
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  Files         286      286           
  Lines       60097    60106    +9     
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+ Hits        50950    50961   +11     
+ Misses       9147     9145    -2