Fix: CDM show buff and target debuff stack count at 1 stack

[daniel-lewinski]

What does this PR do?

Displays the stack count text when a buff or player-applied target debuff is at 1 stack (in addition to 2+ stacks), across Cooldown Manager (BuffIconCooldownViewer) icons, tracking buff bars, and AuraKit engine aura buttons. By default, Blizzard's native aura widgets hide the count text at 0 and 1 stack, only revealing numbers starting from 2 stacks.

Cause

In World of Warcraft (Midnight 12.x):

1. Engine Aura Buttons (EllesmereUI_AuraKit.lua): button:SetApplicationCount(d.stack, {}) is called with empty options, causing Blizzard's internal formatter to default to hiding count text when application count <= 1.
2. CDM Buff/Debuff Icons (EllesmereUICooldownManager.lua): icon.Applications fontstrings rely on Blizzard's internal display logic which suppresses rendering at 1 stack.
3. Tracking Buff Bars (EllesmereUICdmBuffBars.lua): UpdateStacks checks appsText.GetText(appsText). Since Blizzard's native text is empty string "" at 1 stack, bar._stacksText is hidden even though ReadStackApplications(blzChild) reads 1.

Fix

1. AuraKit Stack Formatter (EllesmereUI_AuraKit.lua):

   • Implements AK.GetStackFormatter() using C_StringUtil.CreateNumericRuleFormatter() with breakpoints { threshold = 0, format = "" } and { threshold = 1, format = "%d" }.
   • Passes this formatter to button:SetApplicationCount(d.stack, { formatter = stackFmt }).

2. CDM Single-Stack Display & Mirror (EllesmereUICooldownManager.lua):

   • In RefreshCDMIconAppearance, creates a dedicated overlay FontString mirror (icon._euiStackText) positioned identically to the native stack count text and sets Blizzard's native icon.Applications.Applications alpha to 0.
   • Adds ns.UpdateSingleStackText(icon) which safely resolves application count from icon.auraDataCached.applications or C_UnitAuras.GetAuraDataByAuraInstanceID (guarding against secret values in 12.x combat environments).
   • Hooks lifecycle methods (OnAuraInstanceInfoSet, OnUnitAuraUpdatedEvent, OnUnitAuraAddedEvent, ClearAuraInstanceInfo, OnAuraInstanceInfoCleared, OnCooldownIDSet) on CDM frames once per frame using hooksecurefunc.
   • Registers PLAYER_TARGET_CHANGED on an addon-owned frame to update target debuff single-stack counts when switching targets.
   • Respects showChargeStackText = false (csAlpha == 0).

3. Tracking Buff Bars (EllesmereUICdmBuffBars.lua):

   • In UpdateStacks, falls back to ReadStackApplications(blzChild) if native appsText is empty, showing the stack text when applications are present.

Cost

• Zero OnUpdate polling: completely event-driven via hooksecurefunc on aura lifecycle hooks and PLAYER_TARGET_CHANGED.
• Single-instance formatter cached at file scope in AuraKit.
• Secret-safe handling for 12.x: all numeric checks are guarded with issecretvalue() and pcall, and FontString:SetText() is used as a safe sink.

How was it tested?

• Tested in-game on live client:
  1. Gained a 1-stack buff (e.g. tracking buff on CDM bar / player aura) -> count text "1" correctly displays.
  2. Reapplied / increased stacks to 2+ -> count updates dynamically to "2", "3", etc.
  3. Buff expired / removed -> count text clears properly to empty string.
  4. Applied target debuff at 1 stack -> count text displays "1"; switching targets updates accurately via PLAYER_TARGET_CHANGED.
  5. Verified options toggle Show Charges/Stacks Text: Off (showChargeStackText = false) continues to hide the count text cleanly.

Checklist

• New settings default OFF (no behavior change without opt-in) (N/A - bug fix / parity enhancement for stack display)
• Zero cost while disabled: no events registered, no polling, no hooks doing work, no frames built
• Cheap while enabled: event-driven (no polling, no timer-based logic, no per-frame allocations)
• No writes onto Blizzard-owned frames (weak-table pattern used); HookScript/hooksecurefunc only, never SetScript on Blizzard frames
• Tested in-game on live; no version gates or pre-Midnight APIs added