Save version 0.3.0

This version as been used during many courses up until Jan 2026
While teaching in January 2026 we notices an inconsistency in the way we deal with the time variable (or cycle length) in the rate_to_prob and prob_to_rate.

We same this version for all that used this version to allow to get this work.
The new function will get an update and a warming message to inform users about the new release.

This version can be installed using remotes::install_github("DARTH-git/darthtools@v0.3.0")