fix: add InstructionName, LibVersion, LibName to allowed VAR attributes

SCL005 false positive triggered on:
  timers{InstructionName := 'IEC_TIMER'; LibVersion := '1.0'}
These are valid TIA Portal attributes for IEC timer variables.

src/diagnostics.lua

@@ -109,6 +109,9 @@ function M.validate_diagnostics(content, workspace_types, root_dir)
       EXTERNALWRITABLE = true,  -- all-caps VCI export variant
       EXTERNALVISIBLE = true,   -- all-caps VCI export variant
       EXTERNALACCESSIBLE = true,-- all-caps VCI export variant
+      InstructionName = true,
+      LibVersion = true,
+      LibName = true,
       S7_SetPoint = true,
       S7_Optimized_Access = true,
     }