[proto] Small optims for elastic op on bboxes

[vfdev-5]

[--------- elastic_bounding_box cpu BoundingBoxFormat.XYXY ----------]
            |  elastic_bounding_box_old v2  |  elastic_bounding_box v2
1 threads: -----------------------------------------------------------
      (4,)  |              230              |            190          
6 threads: -----------------------------------------------------------
      (4,)  |              300              |            200          

Times are in microseconds (us).

[--------- elastic_bounding_box cpu BoundingBoxFormat.XYWH ----------]
            |  elastic_bounding_box_old v2  |  elastic_bounding_box v2
1 threads: -----------------------------------------------------------
      (4,)  |              310              |            260          
6 threads: -----------------------------------------------------------
      (4,)  |              330              |            280          

Times are in microseconds (us).

[-------- elastic_bounding_box cpu BoundingBoxFormat.CXCYWH ---------]
            |  elastic_bounding_box_old v2  |  elastic_bounding_box v2
1 threads: -----------------------------------------------------------
      (4,)  |              351              |            300          
6 threads: -----------------------------------------------------------
      (4,)  |              379              |            330          

Times are in microseconds (us).

[--------- elastic_bounding_box cuda BoundingBoxFormat.XYXY ---------]
            |  elastic_bounding_box_old v2  |  elastic_bounding_box v2
1 threads: -----------------------------------------------------------
      (4,)  |              440              |            380          
6 threads: -----------------------------------------------------------
      (4,)  |              440              |            380          

Times are in microseconds (us).

[--------- elastic_bounding_box cuda BoundingBoxFormat.XYWH ---------]
            |  elastic_bounding_box_old v2  |  elastic_bounding_box v2
1 threads: -----------------------------------------------------------
      (4,)  |              560              |            490          
6 threads: -----------------------------------------------------------
      (4,)  |              560              |            490          

Times are in microseconds (us).

[-------- elastic_bounding_box cuda BoundingBoxFormat.CXCYWH --------]
            |  elastic_bounding_box_old v2  |  elastic_bounding_box v2
1 threads: -----------------------------------------------------------
      (4,)  |              640              |            570          
6 threads: -----------------------------------------------------------
      (4,)  |              640              |            570          

Times are in microseconds (us).

cc @datumbox @bjuncek @pmeier

[datumbox]

I benchmarked your intermediate commits and what you have now (along with the proposed patch below) seems the fastest:

[------------------------------- elastic_bounding_box cpu BoundingBoxFormat.XYXY --------------------------------]
            |  elastic_bounding_box main  |  elastic_bounding_box_bbeca bbeca  |  elastic_bounding_box_b32f7 b32f7
1 threads: -------------------------------------------------------------------------------------------------------
      (4,)  |             613             |                575                 |                490               

Times are in microseconds (us).

[------------------------------- elastic_bounding_box cpu BoundingBoxFormat.XYWH --------------------------------]
            |  elastic_bounding_box main  |  elastic_bounding_box_bbeca bbeca  |  elastic_bounding_box_b32f7 b32f7
1 threads: -------------------------------------------------------------------------------------------------------
      (4,)  |             674             |                636                 |                551               

Times are in microseconds (us).

[------------------------------ elastic_bounding_box cpu BoundingBoxFormat.CXCYWH -------------------------------]
            |  elastic_bounding_box main  |  elastic_bounding_box_bbeca bbeca  |  elastic_bounding_box_b32f7 b32f7
1 threads: -------------------------------------------------------------------------------------------------------
      (4,)  |             710             |                676                 |                580               

Times are in microseconds (us).

[------------------------------- elastic_bounding_box cuda BoundingBoxFormat.XYXY -------------------------------]
            |  elastic_bounding_box main  |  elastic_bounding_box_bbeca bbeca  |  elastic_bounding_box_b32f7 b32f7
1 threads: -------------------------------------------------------------------------------------------------------
      (4,)  |             1370            |                1310                |                708               

Times are in microseconds (us).

[------------------------------- elastic_bounding_box cuda BoundingBoxFormat.XYWH -------------------------------]
            |  elastic_bounding_box main  |  elastic_bounding_box_bbeca bbeca  |  elastic_bounding_box_b32f7 b32f7
1 threads: -------------------------------------------------------------------------------------------------------
      (4,)  |             1470            |                1410                |                789               

Times are in microseconds (us).

[------------------------------ elastic_bounding_box cuda BoundingBoxFormat.CXCYWH ------------------------------]
            |  elastic_bounding_box main  |  elastic_bounding_box_bbeca bbeca  |  elastic_bounding_box_b32f7 b32f7
1 threads: -------------------------------------------------------------------------------------------------------
      (4,)  |             1540            |                1480                |                858               

Times are in microseconds (us).

[datumbox]

LGTM, thanks!

[github-actions]

Hey @vfdev-5!

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