[TF2] improve medigun heal target selection to prioritize teammate directly under crosshair when teammates are close together

[wgetJane]

Description

this pr solves a minor annoyance with medic where teammates would block you from being able to heal someone that's close to them

this issue is caused by how the medigun traces for player collision hulls for leniency instead of the more accurate player hitboxes

the solution in this pr is to simply trace a second time for player hitboxes and prioritise the result when applicable

before:

mediguntarget_before.mp4

after:

mediguntarget_after.mp4