Fixes stabilized red bypassing immutable slowdowns / Fixes being unable to construct fulltile objects on immutably slow things (#82250)

## About The Pull Request

- Fixes Stabilized Red extract's equipment slowdown immunity bypassing
item Immutable Slowdown

- Fixes(?) Settler equipment slowdown modifier applying to immutable
slows

- Fixes Immutable Slow being considered an object flag when it was an
item flag, causing objects to consider objects with it to be
`BLOCKS_CONSTRUCTION_DIR`

## Why It's Good For The Game

The description of Immutable Slows: 

`When players should not be able to change the slowdown of the item
(Speed potions, etc)`

Stabilized Red extracts were changing the slowdown of the item, which is
unintended.
Likewise Settler was doing the same, but that one I'm a bit more iffy
on.

Either way I suppose if things should immutably be slow, they should
immutably be slow.

## Changelog

🆑 Melbert
fix: Stabilized Red extracts no longer bypass Immutably Slow items
fix: Settler equipment speed modifier no longer applied to Immutably
Slow items
fix: Immutably Slow items no longer block construction of certain items 
/🆑

code/modules/mining/equipment/mining_tools.dm

@@ -314,8 +314,7 @@
 	pickup_sound = 'sound/items/handling/crowbar_pickup.ogg'
 	hitsound = 'sound/weapons/sonic_jackhammer.ogg'
 	block_sound = 'sound/weapons/sonic_jackhammer.ogg'
-	obj_flags = IMMUTABLE_SLOW
-	item_flags = SLOWS_WHILE_IN_HAND
+	item_flags = SLOWS_WHILE_IN_HAND | IMMUTABLE_SLOW
 	slowdown = 3
 	attack_speed = 1.2 SECONDS
 	/// The factor at which the recoil becomes less.