More methods for round and rand, fix NNlib

[adrhill]

Closes #152.

• Add more methods for round and rand
• Fix Hessians on NNlib activation functions celu, elu, selu and hardswish
• Increase code coverage

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 98.38710% with 1 line in your changes missing coverage. Please review.

Project coverage is 92.70%. Comparing base (c3d2cfb) to head (3bfa3e9).

Files	Patch %	Lines
test/test_hessian.jl	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #162      +/-   ##
==========================================
+ Coverage   91.90%   92.70%   +0.79%     
==========================================
  Files          37       37              
  Lines        1545     1590      +45     
==========================================
+ Hits         1420     1474      +54     
+ Misses        125      116       -9     

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