Final(?) tweaks to ID track silicon seeding
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This MR adds some small further performance tweaks to the seeding phase of ID track reconstruction, as part of the ATLIDTRKCP-260 optimization round:
The changes should leave the tracking efficiency stable at sub-permille level, while the fake rate is reduced by around 10%. The CPU time for the track finding step should improve by slightly below 10 percent, with slight downstream profits to the ambiguity resolution and track extension, and a 3-4% improvement in overall tracking CPU. A detailed discussion of the changes is available in these slides.
Adding @norap and @sroe. Also including @amete for information in case this shows up in SPOT.