Remove a lot of warnings (considered as errors by dune).

nb : i have changed the var name in the generated nodes, which was a bad idea
(=painful to get it rigth again).

Indeed, in order to sort Soc.gao, I currently process in 3 stages ;
1. compute a total ordering of Actions.t according to the deps
2. transform Actions.t into Soc.gao (List.map)
3. factorize Soc.gao by looking at consecutive gao that have the same guard

With this change, between steps 1 and 2, I reorder the list of actions
so that group of independent actions are sorted according to their
clock. The idea is of course to provide to step 3 more opportunities
of factorization.

The result is not very convincing yet.

I've also tried to sort the actions wrt their clock before performing
the toposort. Seems not too bad.

I've kept the old behavior by default though.

Indeed it is possible when each branch of the ite updates no memory.
This is done in the new L2lOptimIte module.

For the time being, it does detect when the node has no memory. It
only looks at the declaration: nodes have memory, and not functions.

I should infer that information and raise warnings or errors if what
I infer is not compatible with waht is declared (will come later).

Also split ActionsDep into ActionsDep and Action.

Also fix a bug in L2lsplit where deeply nested (>2) merge were not
splitted.