ngspice variable count

[sobremesa87]

Output raw files from ngspice sometimes have a form that means variables are not detected correctly by the regular expressions. Like in this example:

"Variables:
0 v-sweep voltage
1 voltage
2 @include[current] capacitance
3 i(@m.xm1.msky130_fd_pr__nfet_01v8_lvt[ib]) current dims=0
...
"

In this case, lines 1 and 2 were merged. Ultimately, this leads to a mismatch between the number of fields in the dtype and the number of fields in the array of values, so the file cannot be read. Have changed from a regular expression to a line by line interpretation to get round this. Also, as in the contribution guidelines, have added some tests for this code. Tests are based on a simulation of the open source skywater library.