Mitigate performance drop when looking up the muon efficiency systematics

Hi,

the merge request !20096 (merged) brought many updates to the MuonEfficiencyCorrections code. However, during the profiling of our code, we noticed that the look-up whether the systematic affects the tool or not takes occupies many resources.

Before:

After:

This merge request tries to address the problem by introducing an extra map storing the systematic variation against the corresponding collection map.

Adding: @goblirsc, @jburr, @dguest, @pgadow and our well admired friend the @atlasbot.