GetUnitWeaponHaveFreeLineOfFire may no longer correctly detect terrain

Previously MCL sector code used a beamlaser weapon and `GetUnitWeaponHaveFreeLineOfFire` to check for terrain, and at some point it worked c.f. https://www.dropbox.com/scl/fi/vode1c0feaurnmubvbtgk/video1.avi?rlkey=rh00xotxslcva5yau1a6gphso&dl=0.

I discovered in the past few days that it no longer worked correctly vs terrain (on recoil_2025.06.21), and swapped for the new `TraceRayGroundBetweenPositions` function

https://github.com/SpringMCLegacy/SpringMCLegacy/commit/510680b124ffe255576de7807a0e3d2ab29ff95a

Caveats;

- The video is from 2016 and much has changed in the game and engine since then.
- The map and setup is different in the video to what I was testing recently (one enemy placed up on a cliff top with friendly at the bottom, moving close to the cliff should make enemy invisible as the cliff gets in the way, I can provide a demo if required)

However, given the minimal change in my commit above, basically just a 1-for-1 replacement it seems there is incongruency between a beamlaser i.e. scanhit weapon's `HaveFreeLineOfFire` and `TraceRayGroundBetweenPositions` when it comes to terrain, which I would not expect.

Start by locating GetUnitWeaponHaveFreeLineOfFire and TraceRayGroundBetweenPositions, then compare how each handles terrain intersection for beamlaser or scanhit weapons. Reproduce the described cliff-top scenario, using commit 510680b124ffe255576de7807a0e3d2ab29ff95a as context; done means line-of-fire terrain detection is consistent with the expected visibility behavior.

Written by the indexing model from the issue text.