Ports various platform sprites (#23054)

As title, ports some sprites from CM as a supplement for our generic
platforms. I wasn't able to find the authors due to how .dmi change
history is stored in git

## Images

<img width="731" height="797" alt="Screenshot_8"
src="https://github.com/user-attachments/assets/fb2cf11e-be85-4e16-b747-00d710fb9b1c"
/>


### Asset Licenses
The following assets that **have not** been created by myself are
included in this PR:

| Path | Original Author | License |
| --- | --- | --- |
| icons/obj/structure/platforms.dmi | Colonial Marines | CC 3.0 BY-SA |

code/modules/multiz/structures.dm

@@ -418,6 +418,8 @@
 /obj/structure/platform_stairs/full/south_north_cap/half
 	icon_state = "p_stair_sn_half_cap"
 
+// ---------- Platforms
+
 /obj/structure/platform
 	name = "platform"
 	desc = "An archaic method of preventing travel along the X and Y axes if you are on a lower point on the Z-axis."
@@ -507,16 +509,58 @@
 	icon_state = "ledge_dark"
 	color = COLOR_DARK_GUNMETAL
 
+/obj/structure/platform/rock
+	icon_state = "colorable_rock_platform"
+	color = COLOR_GRAY40
+
+// ---------- Non-colourable platforms
+
+/obj/structure/platform/metal
+	icon_state = "metal_platform"
+	color = null
+
+/obj/structure/platform/metal_alt
+	icon_state = "metal_platform_alt"
+	color = null
+
+/obj/structure/platform/engineer
+	icon_state = "engineer_platform"
+	color = null
+
+/obj/structure/platform/accented
+	icon_state = "accented_platform"
+	color = null
+
+/obj/structure/platform/column
+	icon_state = "column_platform"
+	color = null
+
+// ---------- Platform cutouts
+
 /obj/structure/platform/cutout
 	icon_state = "platform_cutout"
-	density = 0
+	density = FALSE
+
+/obj/structure/platform/cutout/CanPass()
+	return TRUE
 
 /obj/structure/platform/cutout/dark
 	icon_state = "platform_cutout_dark"
 	color = COLOR_DARK_GUNMETAL
 
-/obj/structure/platform/cutout/CanPass()
-	return TRUE
+/obj/structure/platform/cutout/metal
+	icon_state = "metal_platform_cutout"
+	color = null
+
+/obj/structure/platform/cutout/metal_alt
+	icon_state = "metal_platform_alt_cutout"
+	color = null
+
+/obj/structure/platform/cutout/column
+	icon_state = "column_platform_cutout"
+	color = null
+
+// ---------- Platform decos
 
 /// No special CanPass for this one.
 /obj/structure/platform_deco
@@ -545,3 +589,29 @@
 /obj/structure/platform_deco/ledge/dark
 	icon_state = "ledge_deco_dark"
 	color = COLOR_DARK_GUNMETAL
+
+/obj/structure/platform_deco/rock
+	icon_state = "colorable_rock_platform_deco"
+	color = COLOR_GRAY40
+
+// ---------- Non-colourable platform decos
+
+/obj/structure/platform_deco/metal
+	icon_state = "metal_platform_deco"
+	color = null
+
+/obj/structure/platform_deco/metal_alt
+	icon_state = "metal_platform_alt_deco"
+	color = null
+
+/obj/structure/platform_deco/engineer
+	icon_state = "engineer_platform_deco"
+	color = null
+
+/obj/structure/platform_deco/accented
+	icon_state = "accented_platform_deco"
+	color = null
+
+/obj/structure/platform_deco/column
+	icon_state = "column_platform_deco"
+	color = null