fix: retain observed equations after structural_simplify of SDESystem
#5752
| Job | Run time |
|---|---|
| 49m 4s | |
| 1h 5m 58s | |
| 17m 48s | |
| 51m 26s | |
| 24m 26s | |
| 15m 28s | |
| 40s | |
| 31m 51s | |
| 40s | |
| 19m 25s | |
| 25m 10s | |
| 21m 24s | |
| 15m 39s | |
| 5h 38m 59s |