Update MF7 recipe to latest changes in ENDF-102

[marquezj]

This pull request aims to address two changes were introduced in the description of file 7 in November 2023:

• A new reaction, MF7/MT451, was included to add isotopic information on thermal scattering files. This reaction is called Generalized Information File.
• The thermal elastic reaction, MF7/MT2, was updated to include support for both coherent and incoherent contributions in the "mixed elastic" format.

[gschnabel]

Thank you for this pull request. When you check out the dev branch, you'll see that the package has undergone significant refactoring and the recipes moved to endf_parserpy/endf_recipes/endf6

It would be most convenient for me, if you could create the same pull request on the dev branch to avoid merge conflicts.

[marquezj]

No problem @gschnabel. I will close this one and start a new pull request.