Refactor nameplate cast tracking to be fully GUID-based

Problem:
Since a recent Turtle-WoW update, nameplates would show the same castbar on all mobs sharing a name (e.g. multiple "Defias Rogue Wizard"). Additionally, a targeted mob that was not casting would incorrectly display the castbar of a nearby mob with the same name.

Changes:
**`modules/nameplates.lua`**
- Removed `hasNampower` version-sniffing entirely. Nampower is a hard requirement for pfUI; all related guards have been removed and the code runs unconditionally.
- Castbar lookup now always uses `nameplate.cachedGuid` directly — never `GetUnitGUID("target")` or a unit name string.
- Removed dead fallback block using `UnitCastingInfo("target")`.
- Restored fallback via `pfGetCastInfo(cachedGuid)` / `pfGetChannelInfo(cachedGuid)` (see libcast changes below) for casts not tracked by libdebuff (e.g. already-in-progress casts on login).

**`libs/libcast.lua`**
- Renamed `UnitCastingInfo` → `pfGetCastInfo` and `UnitChannelInfo` → `pfGetChannelInfo` to avoid confusion with the Blizzard API of the same name, which does not exist in Vanilla.
- Name-based fallback lookup (`libcast.db[unitName]`) is now skipped when a GUID is available. This prevents cast bleed between mobs that share a name.

**`libs/libpredict.lua`, `modules/castbar.lua`, `modules/afkcam.lua`**
- Updated all call sites to use the renamed `pfGetCastInfo` / `pfGetChannelInfo`.

libs/libpredict.lua

@@ -446,7 +446,7 @@ function libpredict:ParseComm(sender, msg)
           rank = tonumber(rankStr)
         end
       end
-    elseif select and UnitCastingInfo then
+    elseif select and pfGetCastInfo then
       -- latest healcomm
       msgtype = tonumber(string.sub(msg, 1, 3))
       if not msgtype then return end
@@ -456,8 +456,8 @@ function libpredict:ParseComm(sender, msg)
         heal = tonumber(string.sub(msg, 4, 8))
         target = string.sub(msg,9, -1)
 
-        local starttime = select(5, UnitCastingInfo(sender))
-        local endtime = select(6, UnitCastingInfo(sender))
+        local starttime = select(5, pfGetCastInfo(sender))
+        local endtime = select(6, pfGetCastInfo(sender))
         if not starttime or not endtime then return end
         time = endtime - starttime
       elseif msgtype == 1 then
@@ -466,8 +466,8 @@ function libpredict:ParseComm(sender, msg)
         msgtype = "Heal"
         heal = tonumber(string.sub(msg,4, 8))
         target = {strsplit(":", string.sub(msg,9, -1))}
-        local starttime = select(5, UnitCastingInfo(sender))
-        local endtime = select(6, UnitCastingInfo(sender))
+        local starttime = select(5, pfGetCastInfo(sender))
+        local endtime = select(6, pfGetCastInfo(sender))
         if not starttime or not endtime then return end
         time = endtime - starttime
       end