Improvements on PrStoreUTHit

This MR needs LHCb!1163 (merged)

id is a unique number to identify couple station/layer

current algo : sort (using rv3) ut hits by id first then by x at y=0

here we have swaps on 2 vectors :

• the id vector of MultiIndexedHitContainer
• the hits vector of MultiIndexedHitContainer

as input we have already hits sorted by id

• Remove this sort and replace by a stable sort on x for the 4 layers;
• Also use a constant time getter to get sectors of UT

gain around ~55% on PrStoreUTHit according to callgrind

before; after

recbefore.cg recafter.cg

@sponce