Feature: Have a mixin for log-based and exp-based distributions

[vincent-antaki]

It doesn't have to do anything, it would be useful, when designed fancy hyperparam research strategies, to know with a isinstance call if a distribution is log-based or exp-based. Alternatively, it could be a function (e.g. is_log_based).

[guillaume-chevalier]

Might need to solve this issue to do #464 more easily after.

[stale[bot]]

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