Fix SPIN-JET code for EAGLE
The code wasn't actually compiling due to some missing BH fields/BH io information.
I've added that now but I still can't compile, due to an error that I'm having trouble interpreting:
In file included from ./black_holes_io.h:33:
././black_holes/SPIN_JET/black_holes_io.h:175:17: error: incomplete definition of type 'struct black_holes_props'
175 | props->temp_to_u_factor;
| ~~~~~^
./engine.h:523:16: note: forward declaration of 'struct black_holes_props'
523 | const struct black_holes_props *black_holes_properties;
| ^
1 error generated.