fix: memory leaks in Item wrappers and optimize CustomItems

[MS-crew]

Description

Updated Item.Destroy so if an item isnt actually in an inventory it properly removes it from the dict and forces gameobject destroy so the leak is completely gone.

CustomGrenade.Throw was throwing nres when player was null cause server host doesnt have a camera or fpc role. also it was spawning a whole dummy item just to throw it which is bad for perf so i rewrote it to just use native throwable templates.

CustomWeapon.Spawn was leaving the temporary firearm in memory after creating the pickup. added a destroy call for that.

Fixed genericfirearm damage handler cause ragdolls were only showing bullet wounds and when dying attacker is null from client side. it reads the ammo type directly from the native template module now.

GenerateAttachments was literally spawning every single gun on server startup just to read attachments which is nonsense. changed it to use native templates

fun fact: before this fix, exiled was casually leaving 14 dead firearm objects in memory on server startup before any plugins even did anything. that's completely gone now.

What is the current behavior? (You can also link to an open issue here)

What is the new behavior? (if this is a feature change)

Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

Other information:

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentations

Submission checklist

• I have checked the project can be compiled
• I have tested my changes and it worked as expected

Patches (if there are any changes related to Harmony patches)

• I have checked no IL patching errors in the console

Other

• Still requires more testing