Update a_mu SM and exp

[alekssmolkovic]

This PR updates the SM prediction of a_mu to the one reported here and the FNAL combination in measurements to the one reported here. The FNAL g-2 combination measurement is used in smelli.

[peterstangl]

Thanks!

For the measurement, I think we should add a new entry that contains the year in the name, e.g. FNAL g-2 combination 2025 instead of modifying the old measurement, which would break backwards compatibility. Otherwise, old results in existing code could not be reproduced anymore. Please also include the inspire: field in the new entry.

I think the tests also have to be updated.