Make Numba an optional dependency

[beat-buesser]

Signed-off-by: Beat Buesser beat.buesser@ie.ibm.com

Description

This pull request make Numba an optional dependency.

Fixes #1875

Type of change

Please check all relevant options.

• Improvement (non-breaking)
• Bug fix (non-breaking)
• New feature (non-breaking)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

[codecov-commenter]

Codecov Report

Merging #1884 (093cbfb) into dev_1.12.2 (3e3a438) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@              Coverage Diff               @@
##           dev_1.12.2    #1884      +/-   ##
==============================================
- Coverage       85.90%   85.89%   -0.02%     
==============================================
  Files             248      248              
  Lines           23312    23312              
  Branches         4212     4212              
==============================================
- Hits            20027    20024       -3     
- Misses           2224     2226       +2     
- Partials         1061     1062       +1     

Impacted Files	Coverage Δ
art/estimators/certification/abstain.py	90.90% <0.00%> (-9.10%)	⬇️
art/estimators/poison_mitigation/strip/strip.py	94.44% <0.00%> (-5.56%)	⬇️