Major fix of type unstabilities which improved performances.
For now on, we observe for pygmalion benchmarks:
+2x speed simulation compared to simulation of models.
100x speed in terms of reading values (no allocations).

- a script to run the different categories
- now the execution of simulation/ scripts is checked
- several minor changes and add of tests

New directory : models/_bench_perf_tests.  Models for performance benchmarking purposes.

- Add of benchmark scripts that compares perf wrt pygmalion.
=> As expected it is bad in terms of reading cost (because of row by row
matrix read) but it is also not good in terms of simulation cost.
hcat seems to perform badly, should investigate.