Remove redundant POLYESTER_LOADED flag

When Polyester is loaded, RecursiveArrayToolsFastBroadcastPolyesterExt
defines more-specific methods for AbstractVectorOfSArray that win
dispatch, so the base ext's AbstractVectorOfArray fallback is only
reached when Polyester is not loaded. The flag check was redundant.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ChrisRackauckas

ext/RecursiveArrayToolsFastBroadcastExt.jl

@@ -36,7 +36,10 @@ end
         ::Threaded, dst::AbstractVectorOfArray,
         bc::Broadcast.Broadcasted
     )
-    if dst isa AbstractVectorOfSArray && !RecursiveArrayTools.POLYESTER_LOADED[]
+    # When Polyester is loaded, RecursiveArrayToolsFastBroadcastPolyesterExt
+    # defines more-specific methods for AbstractVectorOfSArray, so reaching
+    # this method with an SArray VoA means Polyester is not loaded.
+    if dst isa AbstractVectorOfSArray
         error("Threaded FastBroadcast on VectorOfArray{SArray} requires Polyester.jl. " *
               "Add `using Polyester` to enable threaded broadcasting, or use " *
               "`@.. thread=false` for serial broadcasting.")

ext/RecursiveArrayToolsFastBroadcastPolyesterExt.jl

@@ -6,9 +6,6 @@ using FastBroadcast: Serial, Threaded
 using Polyester
 using StaticArraysCore
 
-# Signal to the base FastBroadcast extension that Polyester threading is available.
-RecursiveArrayTools.POLYESTER_LOADED[] = true
-
 const AbstractVectorOfSArray = AbstractVectorOfArray{
     T, N, <:AbstractVector{<:StaticArraysCore.SArray},
 } where {T, N}

src/RecursiveArrayTools.jl

@@ -195,11 +195,6 @@ module RecursiveArrayTools
 
     export ArrayPartition, AP, NamedArrayPartition
 
-    # Flag set to `true` by RecursiveArrayToolsFastBroadcastPolyesterExt when
-    # Polyester is loaded. Checked by the FastBroadcast ext to decide whether
-    # to throw an informative error on threaded VoA{SArray} operations.
-    const POLYESTER_LOADED = Ref(false)
-
     include("precompilation.jl")
 
 end # module