Lifetime broadening makes calculation run 180 times slower

[ajm143]

Describe the bug
Whilst working on the MZ correction we found that lifetime broadening make the NaGe core-loss calculation take minutes, rather than seconds. I need to investigate if there's something that can speed it up. Is there something sub-optimal in the loops?

To Reproduce
Add LAI broadening to a CORE calc.

Expected behavior
it should be faster!

[ajm143]

Bin Spacing. Time w/o LAI. Time w. LAI
0.1. 1.1s 2.7s
0.05 2.2s 9.2s
0.025 4.3s 35.0s

Makes sense as we're doing nbin*nbin operations for the convolution