Add crossing angle to crossing element for unambiguous layouting
The railML 3.3 data model of the (simple) crossing does not allow an unambiguous layouting of the (simple) crossing.
## Links
* Forum discussion:
* Torben Brand, 27.10.2025: https://www.railml.org/forum/index.php?t=msg&goto=3922&#msg_3922
* Gitlab issues:
* #719
* #685
* Wiki documentation:
* IS:crossing: https://wiki3.railml.org/wiki/IS:crossing
## Proposed solution in railML 3.4
Add mandatory child element `<ratio>` to element `<crossing>`.
The `<ratio>` has the mandatory attributes:
* `@fromNetElement` referencing the netElement on which the crossing is located on by spotLocation
* `@toNetElement` referencing the (crossing) neElement that is closest to the first netElement (in any direction)
* `@denominator` describing the ratio as tangens of the crossing angle (0<angle<90 degrees) opened by the two referenced netElements in a mathematical positive orientation. For a crossing angle of 90 degrees (ratio is infinite) the denominator shall be set to the value "0"
issue