More slight parry and dodge changes. (#5712)

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## About The Pull Request
Slightly changes the speed calculation on hitting dodgers.
Instead of your speed/5 rounded down giving them a penalty to dodge,
it's your speed/4 rounded down.
So 12 for example speed now gives them a -3 instead of 15 speed.

Re-implements losing your parry ability when you aggro grab someone, so
you can't aggro grab with one hand and parry all their hits with the
other.

This prevents maniacs and such just aggro-grabbing you, parrying all
your attacks with their knife whilst also making 35 more stab hole
looking nostrils into your face. You can actually stab them back.

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:cl:
balance: Slight rebalance of dodge opposition
fix: Fixes aggro grab parry back to the old state. (The removal was
never mentioned? Not sure if intended.)
/:cl:

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- [x] You tested this on a local server.
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Author: Rockslp

code/modules/mob/living/dodge.dm

@@ -102,8 +102,7 @@
 	var/dodge_speed = floor(GET_MOB_ATTRIBUTE_VALUE(src, STAT_SPEED) / 2)
 
 	// fast attackers raise the threshold (mirror of parry system)
-	// STAT_SPEED on 0-~30 range; divide by 5 for ~0-6 opposition impact
-	var/attacker_opposition = floor(GET_MOB_ATTRIBUTE_VALUE(user, STAT_SPEED) / 5)
+	var/attacker_opposition = floor(GET_MOB_ATTRIBUTE_VALUE(user, STAT_SPEED) / 4)
 
 	if(istype(src, /mob/living/carbon/human))
 		var/mob/living/carbon/human/H = src

code/modules/mob/living/parry.dm

@@ -35,6 +35,8 @@
 		return FALSE
 	if(intenty && !intenty.canparry)
 		return FALSE
+	if(pulling && grab_state >= GRAB_AGGRESSIVE)
+		return FALSE
 	if(incapacitated())
 		return FALSE
 	if(has_status_effect(/datum/status_effect/debuff/exposed))