More robust rand_laplace implementation

[zeotuan]

Proposed changes

After adding some test I found that the rand_laplace implementation provide slightly wrong distribution. So this PR aim to use a more robust implementation and add test to verify the mean and standard deviation of the generated sample

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

[SemyonSinchenko]

Thanks for fixing it! LGTM