Reduce coupling in the `MjParse`

[volodya-lombrozo]

Currently MjParse mixes Maven entry-point concerns with core EO-to-XMIR parsing logic, making it hard to test in isolation.

It would be nice to decouple MjParse similar to what was done in #4989 for MjResolve and #5061 for MjTranspile:

1. MjParse - a thin Maven endpoint.
2. Parse - core parsing logic without Maven dependencies.

Also, it's important to find out if it's possible to remove the dependency on Maven-specific fields (e.g. PluginDescriptor) entirely from the core class.