Improving Mixed precision experience

[ofirgo]

Pull Request Description:

Several minor modifications to Mixed Precision to improve the user experience and stability:

• Disabling Hessian-based weights for a mixed precision metric by default (reduce run-time significantly and improve consistency)
• Modifying distance metric to take the maximal value between the maximal configuration value and other computed values with additional epsilon, for numerical stability.
• Adding a convenient API for choosing a distance metric weighting method (MpDistanceWeighting enum) - enables to use the last-layer metric which, in some cases, can produce more consistent results.
• Improve results logging.
• Remove default mp config object (unused and can cause confusion).
• Slight modification to mixed precision tests.

Checklist before requesting a review:

• I set the appropriate labels on the pull request.
• I have added/updated the release note draft (if necessary).
• I have updated the documentation to reflect my changes (if necessary).
• All function and files are well documented.
• All function and classes have type hints.
• There is a licenses in all file.
• The function and variable names are informative.
• I have checked for code duplications.
• I have added new unittest (if necessary).

[eladc-git]

Some small comments.