Not THAT Slow - Update Movespeed Modifiers for Smooth Movement (#22127)

The /tg/-style movespeed_modifier datums were not incorporated into the
original smooth movement PR. While
https://github.com/Aurorastation/Aurora.3/pull/22043 restores that
functionality, the original values no longer feel good now that we're on
smooth movement. This PR halves ALL movespeed_modifier/slowdown datums,
with the exception of species-native, as a baseline before more
individual adjustments are made.

code/game/objects/structures/ECD.dm

@@ -10,7 +10,7 @@
 	anchored = TRUE
 	density = TRUE
 	var/state = ECD_WELDED
-	slowdown = 10
+	slowdown = 5
 	layer = ABOVE_HUMAN_LAYER
 
 /obj/structure/ecd/examine(mob/user, distance, is_adjacent, infix, suffix, show_extended)

code/game/objects/structures/carts/parcelcart.dm

@@ -85,9 +85,9 @@
 	if(my_parcels.len <= 4)
 		slowdown = 0
 	else if(my_parcels.len > 4 && my_parcels.len < 11)
-		slowdown = 1
+		slowdown = 0.5
 	else if(my_parcels.len >= 11)
-		slowdown = 2
+		slowdown = 1
 
 /obj/structure/cart/storage/parcelcart/attack_hand(mob/user)
 	if(!isliving(user))

code/game/objects/structures/crates_lockers/closets.dm

@@ -5,7 +5,7 @@
 	icon_state = "generic"
 	density = TRUE
 	build_amt = 2
-	slowdown = 5
+	slowdown = 2.5
 	pass_flags_self = PASSSTRUCTURE | LETPASSCLICKS | PASSTRACE
 
 	var/icon_door = null

code/game/objects/structures/stool_bed_chair_nest/bed.dm

@@ -38,7 +38,7 @@
 	gfi_layer_rotation = GFI_ROTATION_DEFDIR
 	var/makes_rolling_sound = FALSE
 	var/held_item = null // Set to null if you don't want people to pick this up.
-	slowdown = 5
+	slowdown = 2.5
 
 	var/driving = FALSE // Shit for wheelchairs. Doesn't really get used here, but it's for code cleanliness.
 	var/mob/living/pulling = null

code/game/objects/structures/stool_bed_chair_nest/wheelchair.dm

@@ -8,7 +8,7 @@
 	held_item = /obj/item/material/stool/chair/wheelchair
 	withdraw_verb = "fold"
 	can_dismantle = FALSE
-	slowdown = 1
+	slowdown = 0.5
 
 	var/bloodiness