feat: add output_null_get_bytes jets and update C backend

Add 6 new `output_null_get_bytes_{1,2,4,16,32,64}` jets for reading bytes from OP_RETURN outputs, update the C backend to revision 772dacb, extract jets into a dedicated `jets_wrapper.c` file, and drop the `rustsimplicity_0_6_` prefix from C wrapper symbol names.

Author: stringhandler