[perf][refactor] Clean and improve CerestCostFunctions

Nicolas Cadartrequested to merge
CleanCeresCostFunctions into master

This file has been massively improved in SLAM MR 28.

These changes clean, simplify and greatly accelerate Ceres Residuals (~40%).

This MR aims at reporting these changes in LVCore.

@nick.laurenson @julia.sanchez @lea.vauchier @jerome.dias @melanie.carriere PTAL

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