✨ feat: add a new bs.fsm module

[theogiraudet]

Description

Related Issues

Additional Notes

Tasks to complete before merging

• I agree to release my contribution under the MPL v2 License.
• My pull request is associated with an existing issue.
• I have updated the changelog to reflect my contribution.
• If this pull request adds or modifies a feature:
  • I have documented my changes in the /docs folder.
  • I have updated the metadata of the feature. See feature metadata.
  • I have thoroughly tested my changes. See testing guidelines.

[theogiraudet]

@aksiome if you want to give a first feedback on the API.
I already implemented most of the code, we can currently use FSM and you have an example with bs.fsm:test if you want to try.
I also have more ideas I want to realize:

• Currently, final states are mandatory but this is not the case for every FSMs. I want to propose two different types of FSM: simple FSM (without final states) and acceptors (with final states). I don't know if this is better to define two different features for that, or the same one with a mandatory parameter "type".
• I plan a "hook" transition type, but I think this is something we have to discuss since we wanted to implement such system for other modules.
• I don't know if this is better to have splitted creation/starting as in the current state (features start and new) or to merge those two. The advantages to have them splitted is we can reuse a same definition for several instances, without having to reexecute the validation. But this is also a bit more compilated for users I suppose.