Vcs/zoom rectangle 3

[anisometropie]

closes OpenRailAssociation/osrd#10960

y scale requirements

• min zoom => the entire path is shown
  the scale min zoom metre/px value depends on the length of the path (which is not the case with the time axis, which are constants)
• max zoom => the entire height of the manchette is 500 meter.

map yZoom -> mm/px scale

Previously, yZoom was used as a multiplier. yScale was just changed by increments of 0.5 (using the + or - buttons) and the height in pixel was just multiplied by yScale. This approach is not enough as we need to be able to navigate arbitrary zoom levels and to know how much the size of a rectangle means in term of yZoom.
To do that we need functions to map back and forth between the yZoom level and the value of the scale in mm/px.
this is what zoomValueToSpaceScale spaceScaleToZoomValue do.

seeing that with the min zoom level we need to display the entire path, min Zoom scale value also depends on the length of the path. min and max scale values are given by getExtremaScales

in non proportional mode (linear, every stop has the same height on the manchette), we’re not using a mm/px scale. We directly convert rectangle px height (extended to the full chart height) means in term of stop height.

scale example:
in our story with path of 168 km and manchette height = 528 px, we get min zoom scale of 318287 m/px.

zoom level	mm/px
1	343672
10,5	946

https://www.desmos.com/calculator/o1cq38zueu?lang=fr