Reduce number of calls to 'BicubicSplines'

As shown in the presentations by Nikos or by me, there are currently a lot of calls to the BicubicSplines class, which is used for the evaluation of interpolation tables.

Some of the issues causing the behavior have already been identified.

This will probably be vastly improved just by changes on the PROPOSAL side, as discussed and worked on in this PROPOSAL MR. This fix will be included in the next release of PROPOSAL. After including this in CORSIKA 8, we should re-evaluate how the situation looks like.

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