fix: Godot 4.2.1 compat and map builder fixes

- Fix tab character in _build_elevated_walkways() call (line 63)
- Fix untyped 'pos' variable in grapple pillar loop (line 376)
- Remove fog_sky_affinity (Godot 4.3+ only property)
- Replace preload() with load() for runtime script loading
- Replace 'is DoubleBarrelShotgun' type check with duck-typing
- Fix 'is not OfflineMultiplayerPeer' syntax in grenade spawn
- Replace absf() with abs() in state_machine, state_air, state_ground
- Update test_level.tscn to remove stale UID reference

All fixes verified: PARSE OK and scene runs without script errors
on Godot 4.2.1 headless.

scenes/test_level.tscn

@@ -1,6 +1,6 @@
-[gd_scene format=3 uid="uid://pp1g1inidixa"]
+[gd_scene format=3]
 
-[ext_resource type="Script" uid="uid://c7ltcn37gfd71" path="res://debug/test_level_builder.gd" id="1_2venv"]
+[ext_resource type="Script" path="res://debug/test_level_builder.gd" id="1"]
 
-[node name="TestLevel" type="Node3D" unique_id=130984349]
-script = ExtResource("1_2venv")
+[node name="TestLevel" type="Node3D"]
+script = ExtResource("1")