Previously, we stored the source `mjSpec` during a copy as a hack for having access to the compiler options, but this is not robust since we cannot guarantee that 1) the source `mjSpec` is not destroyed before we need to look up the compiler options nor 2) that the `mjSpec` was appended without a copy.
While 2) could be solved by simply handling an additional case in `mjCModel::FindSpec`, using a map also solves 1) and it is easier to understand.
PiperOrigin-RevId: 741504264
Change-Id: Iab1bfd9e61299a94fa8caf3a244c067b09d54384
Alessio Quaglino
01d4c46753