Draft: Use arrays in HybridSeeding

Related to !3544 (closed) upon which it builds.

Changes the structure of the xHits, making hit order more explicit, a la Allen. This allows for a much more compact clone removal. This leads to a 3-fold acceleration of the seeding in lead-lead.

Finally, in the course of the development of this MR, some options seemed to decrease the number of output tracks quite substantially, leading to an overall speed-up of 8 and a slight reduction in ghost rate (down to 91%). This is being investigated.

Master:

SeedTrackChecker_1b1d5575              INFO Results
SeedTrackChecker_1b1d5575              INFO **** Seed                          1907627 tracks including        1822148 ghosts [95.52 %], Event average 36.46 % ****
SeedTrackChecker_1b1d5575              INFO   01_hasT                        :   64531 from   141610 [ 45.57 %]     37 clones [ 0.06 %], purity: 97.91 %, hitEff: 93.39 %
SeedTrackChecker_1b1d5575              INFO   02_long                        :   32654 from    61355 [ 53.22 %]     11 clones [ 0.03 %], purity: 98.32 %, hitEff: 94.19 %
SeedTrackChecker_1b1d5575              INFO   03_long_P>5GeV                 :   19582 from    35755 [ 54.77 %]      6 clones [ 0.03 %], purity: 98.28 %, hitEff: 94.89 %
SeedTrackChecker_1b1d5575              INFO   06_UT+T_strange                :    5869 from    11204 [ 52.38 %]      4 clones [ 0.07 %], purity: 98.27 %, hitEff: 93.71 %
SeedTrackChecker_1b1d5575              INFO   07_UT+T_strange_P>5GeV         :    3070 from     5711 [ 53.76 %]      2 clones [ 0.07 %], purity: 98.12 %, hitEff: 94.63 %
SeedTrackChecker_1b1d5575              INFO   08_noVelo+UT+T_strange         :    3940 from     7605 [ 51.81 %]      4 clones [ 0.10 %], purity: 98.25 %, hitEff: 93.73 %
SeedTrackChecker_1b1d5575              INFO   09_noVelo+UT+T_strange_P>5GeV  :    2189 from     4138 [ 52.90 %]      2 clones [ 0.09 %], purity: 98.09 %, hitEff: 94.51 %
SeedTrackChecker_1b1d5575              INFO   13_hasT_electrons              :    9741 from    33056 [ 29.47 %]      6 clones [ 0.06 %], purity: 97.92 %, hitEff: 92.04 %
SeedTrackChecker_1b1d5575              INFO   14_long_electrons              :    1042 from     1881 [ 55.40 %]      0 clones [ 0.00 %], purity: 98.16 %, hitEff: 92.07 %
SeedTrackChecker_1b1d5575              INFO   16_long_electrons_P>5GeV       :     377 from      664 [ 56.78 %]      0 clones [ 0.00 %], purity: 97.88 %, hitEff: 94.08 %

 | Sum of all Algorithms                                           |             500 |         961.427 |      1922853.876 |
 | "PrHybridSeeding_4d0337cc"                                      |             378 |         279.906 |       740490.902 |

This branch:

SeedTrackChecker_1b1d5575              INFO Results
SeedTrackChecker_1b1d5575              INFO **** Seed                          1843323 tracks including        1757231 ghosts [95.33 %], Event average 36.58 % ****
SeedTrackChecker_1b1d5575              INFO   01_hasT                        :   65370 from   141610 [ 46.16 %]     68 clones [ 0.10 %], purity: 97.89 %, hitEff: 93.23 %
SeedTrackChecker_1b1d5575              INFO   02_long                        :   33149 from    61355 [ 54.03 %]     29 clones [ 0.09 %], purity: 98.30 %, hitEff: 94.05 %
SeedTrackChecker_1b1d5575              INFO   03_long_P>5GeV                 :   19792 from    35755 [ 55.35 %]     13 clones [ 0.07 %], purity: 98.27 %, hitEff: 94.79 %
SeedTrackChecker_1b1d5575              INFO   06_UT+T_strange                :    5974 from    11204 [ 53.32 %]      6 clones [ 0.10 %], purity: 98.25 %, hitEff: 93.55 %
SeedTrackChecker_1b1d5575              INFO   07_UT+T_strange_P>5GeV         :    3099 from     5711 [ 54.26 %]      3 clones [ 0.10 %], purity: 98.11 %, hitEff: 94.49 %
SeedTrackChecker_1b1d5575              INFO   08_noVelo+UT+T_strange         :    4009 from     7605 [ 52.72 %]      5 clones [ 0.12 %], purity: 98.23 %, hitEff: 93.55 %
SeedTrackChecker_1b1d5575              INFO   09_noVelo+UT+T_strange_P>5GeV  :    2202 from     4138 [ 53.21 %]      2 clones [ 0.09 %], purity: 98.10 %, hitEff: 94.38 %
SeedTrackChecker_1b1d5575              INFO   13_hasT_electrons              :    9970 from    33056 [ 30.16 %]     16 clones [ 0.16 %], purity: 97.85 %, hitEff: 91.79 %
SeedTrackChecker_1b1d5575              INFO   14_long_electrons              :    1067 from     1881 [ 56.73 %]      0 clones [ 0.00 %], purity: 98.09 %, hitEff: 91.92 %
SeedTrackChecker_1b1d5575              INFO   16_long_electrons_P>5GeV       :     383 from      664 [ 57.68 %]      0 clones [ 0.00 %], purity: 97.82 %, hitEff: 93.80 %

 | Sum of all Algorithms                                           |             500 |         771.014 |      1542027.280 |
 | "PrHybridSeeding_4d0337cc"                                      |             378 |          85.437 |       226023.283 |

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