Fill in remaining axioms

[SquidDev]

There's a fair few lemmas and definitions within the codebase which are axiomised, and would be good to fill in:

Species

• Some decision procedure for species equivalence.
• Prime decomposition of species. Here we mostly need to be able to show things like is_prime nil.

Transitions

• transition.rename_from - Effectively undoes a transition - if we have (rename A) —[a]→ E, then there is some a', E' such that rename a' = a, and likewise for E'.
• Show that transition.equivalent_of is a bijection.
• Provide some way of enumerating over every transition. Ideally as a fintype, but as a multiset/finset otherwise.
• Decision procedure for transition equality.

Semantics

• Show appropriate equalities for dP/dt and ∂P under ≡⁺.
• Show process spaces are embedded in processes.

Non-cπ related

• fin_fn.bind_distrib (fin_fn.bind distributes over +)
• fin_fn.bind₂_swap (fin_fn.bind₂ can be swapped).