Seed handling

[astamm]

This is a bad practice to set the seed via an optional argument.
It is usually advised to let the user decide and use {withr} for handling seeds without modifying the user's local environment.
For the plausibility function, it is important to assess its value for each value of the parameters of interest using the same permutations.
@ManonSimonot can you investigate the possible of removing the seed argument in favour of the argument nperm which could be:

• either an integer value in which case nperm permutations are randomly drawn;
• or a list of permutations that would have been previously sampled and stored;
• or a vector of integers giving the random indices of permutations to select within the list of all possible permutations (more memory-efficient than second option).