Armour damage reduction and durability in combat

[xRookieFight]

Problem

Armour items are registered (item/armor.v) but session/combat.v never reads them. Wearing a full set of diamond armour does not reduce incoming damage, armour points are not shown, armour toughness is unused, and armour takes no durability damage when it absorbs a hit.

Proposed solution

• Compute armour points and toughness from the equipped armour slots and apply the vanilla damage reduction formula.
• Send the armour attribute so the client displays it.
• Damage armour durability on hit and break pieces at zero, with the break sound.
• Skip reduction for damage types that bypass armour, and apply protection enchantments once enchantment effects exist.

Scope

session/combat.v, item/armor.v, item/durability.v, player/attributes.v.

[xRookieFight]

Work on this is open as #149.