fix(cdm): let a tracked bar find its debuff on the target

[dfrisone]

Reported by @guld (Cooldown Manager, 9.1.6, so this is current). A common
M+ rogue macro:

/focus target
/cleartarget
/targetenemy
/cast Blind
/target focus
/clearfocus

After pressing it, the player's bleeds on the target stop showing on the
tracked bar until they manually switch target and back.

The stall is Blizzard's

CooldownViewerMixin:OnPlayerTargetChanged only refreshes when the target GUID
differs from the one it stored:

if not self.hasDoneInitialTargetUpdate or self.currentTarget ~= currentTarget then

The macro nets GUID(A) -> nil -> GUID(B) -> GUID(A). Any target-changed event
dispatched after the macro body reads A, matches the stored A, and returns
without calling RefreshActiveFramesForTargetChange, which is the only thing
that re-drives the items. Switching away and back manually produces two
GUID-different edges, which is exactly why that workaround works.

Its GetUnitAurasCached is also keyed on unit token and stamped with
GetTime(), and the only thing that marks it dirty is OnUnitAura, never a
target change -- so two target changes inside one frame leave the later read
returning the stale list.

Why ours goes quiet with it, and what changes

EUI's tracked bars are a stateless per-tick mirror of blzChild:IsActive(),
with no unit, GUID or latch of our own, so when Blizzard's item goes inactive
we follow it down. (The viewer is parked offscreen rather than hidden, which is
correct and stays that way -- hiding it would unregister its own UNIT_AURA
and PLAYER_TARGET_CHANGED.)

There is already a bind-miss fallback for "the viewer has not bound this aura
yet", but it only asked GetPlayerAuraBySpellID, which by definition cannot
see a debuff on somebody else. It now asks the target as well, so the bar rides
out the stall instead of waiting for a real target switch.

Two details worth review:

• Only a readable sourceUnit mismatch rejects the aura. That field reads
  secret on an enemy in restricted content, so an unreadable one is left to
  show rather than blanking the bar; a readable one belonging to another player
  is dropped so their copy of the same debuff cannot drive it.
• No new secret handling was needed downstream. The consumer already classifies
  duration, expirationTime and applications with issecretvalue before
  comparing them.

PLAYER_TARGET_CHANGED also joins both tick wake sets. Target-applied auras
bind and release on that edge and on no player-scoped one, so a parked ticker
previously had no way to learn that a newly selected target already carried a
tracked debuff.

Testing

luac -p clean on both files; house style check clean. Not click-tested. The
reproduction is the macro above with a bleed running; the check is that the bar
survives it without a manual target switch. Worth confirming separately that
another player's copy of the same debuff does not light the bar.