fix(Core/Spells): several improvements to cooldowns (#7559)

- Reworked spell category cooldowns.
- Implemented category cooldowns for pets.
- Properly shows pet spell cooldowns in player's UI.
- Corrected pet spell cooldowns with infinity duration.
- Do not add/remove infinity spell cooldown on aura apply/remove if casted by item.
- Closes #5263

src/server/game/Handlers/PetHandler.cpp

@@ -733,7 +733,7 @@ void WorldSession::HandlePetActionHelper(Unit* pet, ObjectGuid guid1, uint32 spe
 
                 if (result == SPELL_CAST_OK)
                 {
-                    pet->ToCreature()->AddSpellCooldown(spellid, 0, 0);
+                    pet->ToCreature()->AddSpellCooldown(spellid, 0, spellInfo->IsCooldownStartedOnEvent() ? infinityCooldownDelay : 0);
 
                     unit_target = spell->m_targets.GetUnitTarget();