Silent parsing error with sdef

[MicahGale]

Describe the bug

MontePy silently misparses an SDEF input leading to a silently broken input file.

To Reproduce

A short code snippet of what you have ran. Please change or remove any specific values or anything that can't be public. For example:

problem = montepy.read_input("foo.imcnp")
print(problem.data_inputs[-1]._tree.format())

This leads to:

(Node: data: {'start_pad': (Padding, []), 'classifier': (Classifier: mod: None, prefix: (Value, d, padding: None), number: (Value, 5, padding: None), particles: None), 'keyword': (Value, None, padding: None), 'data': (list: empty data, [])})

MCNP input file snippet

1 1 20
         -1000  $ dollar comment
        imp:n,p=1 U=350 trcl=5

C surfaces
1000 SO 1

C data
sdef  cel=d1 erg=d2 pos=fcel d3 ext=fcel d4 axs=0 0 1
     rad=d5

Version

• Version 0.2.5