Tweaks to furniture bridges

[Night-Pryanik]

Summary

Bugfixes "Tweaks to furniture bridges"

Purpose of change

Fix several bugs I noticed.

Describe the solution

• Don't apply increased stamina burn when walking or waiting on "furniture bridges".
• Don't apply slowing down when walking over "furniture bridges". Most bridges are supposed to be easy to move on, so I set base move cost of "furniture bridges" to 2 (like ordinary bridge terrain) + their move_cost_mod. At the time of writing our sole "furniture bridge" (scrap metal bridge) is indeed easy to move on, so its move_cost_mod is 0. In the future we might add more difficult to move versions of such bridges, like rope suspension bridges, with higher move_cost_mod.
  

Describe alternatives you've considered

None.

Testing

Walked over scrap metal bridge. Checked stamina burn. Checked movement cost.

Additional context

None.