Filter unit events with RegisterUnitEvent

ClassicAPI's RegisterUnitEvent registers for an event but only delivers it
when arg1 is one of the given units, so a handler for one unit stops waking
for every other one in the world. Convert the 26 registrations whose unit set
is fixed and known at registration time.

The rule throughout is register the superset and keep the handler's own
check: the filter narrows what arrives, it does not decide what to act on.
castbar is the case that matters -- the player's own casts only ever fire
arg1=="player", never "target"/"focus", so the target and focus bars must
register "player" too, and their UnitIsUnit test is what still rejects a
"player" event while you are targeting a mob.

Two that are not one-line swaps:

  actionbar's two unit events are keys in tables that also drive dispatch, so
  they cannot leave the tables -- and they cannot be plain-registered first,
  because a registration keeps its kind and RegisterUnitEvent over a plain
  one stays plain. They route through a small event_units map instead.

  swingtimer's UNIT_DIED carries a GUID, not a token. The filter is a plain
  case-insensitive string compare with no GUID resolution, so the player's
  own GUID -- fixed for the session -- filters it exactly.

Guards that are now unreachable stay put: the filter applies only when arg1
is a string, so an event that ever fires with a number or no argument is
delivered as if plainly registered, and the handler's own test is what still
rejects it.

Left alone: api/unitframes.lua (the frame's unit changes at runtime and the
handler also matches on GUID), nameplates' six nameplateN events, libdebuff
and libpredict's UNIT_HEALTH (genuinely any unit), and raid.lua's UNIT_PET
(any raid member can own the pet).

modules/actionbar.lua

@@ -807,10 +807,28 @@ pfUI:RegisterModule("actionbar", function ()
 
   -- create the main event and update handler for pfUI actionbars
   local bars = CreateFrame("Frame", "pfActionBar", UIParent)
-  for event in pairs(special_events) do bars:RegisterEvent(event) end
-  for event in pairs(global_events) do bars:RegisterEvent(event) end
-  for event in pairs(aura_events) do bars:RegisterEvent(event) end
-  for event in pairs(pet_events) do bars:RegisterEvent(event) end
+
+  -- The only unit events in the tables above; both concern the player alone.
+  -- A registration keeps its kind, so these have to go in unit-filtered from
+  -- the start -- RegisterUnitEvent over a plain registration stays plain.
+  local event_units = {
+    ["UNIT_INVENTORY_CHANGED"] = "player",
+    ["UNIT_PET"] = "player",
+  }
+
+  local function RegisterBarEvent(event)
+    local unit = event_units[event]
+    if unit then
+      bars:RegisterUnitEvent(event, unit)
+    else
+      bars:RegisterEvent(event)
+    end
+  end
+
+  for event in pairs(special_events) do RegisterBarEvent(event) end
+  for event in pairs(global_events) do RegisterBarEvent(event) end
+  for event in pairs(aura_events) do RegisterBarEvent(event) end
+  for event in pairs(pet_events) do RegisterBarEvent(event) end
 
   -- refresh actionbar buttons on event
   bars:SetScript("OnEvent", BarsEvent)