Support for >1 Interpolation Region in MF=6 LAW=1

Nobody has claimed this yet.

I am working with a JENDL-5 proton evaluation for Li-7 with the goal of extracting File 6 photon production data for analysis ([the file](https://wwwndc.jaea.go.jp/cgi-bin/UNZIP_jendl.cgi?/JENDL/jendl5-p/p_003-Li-007.dat.gz))

Upon execution of
```
from brownies.legacy.converting import endfFileToGNDS

endfFileToGNDS.endfFileToGNDS(
"p_Li7_ENDF.txt",
singleMTOnly=5,
doCovariances=False,
)
```
The converter raises: "Currently only one interpolation region is supported for MF = 6, LAW = 1, LANG = 2; MT = 5"

This impacted gamma product in MF=6/MT=5 has LAW=1, and LANG=1, with two incident-energy interpolation regions (INT=2 below 10 MeV, and INT=22 above). I believe that the LANG=2 in the exception could be a typo. Regardless, is support for multiple-incident energy interpolation regions currently planned?

Thanks!!

Start by running brownies.legacy.converting.endfFileToGNDS with the p_Li7_ENDF.txt input and the shown singleMTOnly=5, doCovariances=False options. Trace the MF=6, LAW=1 interpolation-region handling and verify that the Li-7 MT=5 data with two incident-energy regions converts without the current exception; also check whether LANG=2 in the message is accurate.

Written by the indexing model from the issue text.