Add issparse method for AbstractVectorOfArray

Fixes #486

When issparse(::SubArray) is called, it tries to call issparse on the
parent array. If the parent is an AbstractVectorOfArray, there was no
issparse method defined, causing a MethodError.

This commit adds issparse method that returns false for
AbstractVectorOfArray, since it is not a sparse array type.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: ChrisRackauckas

ext/RecursiveArrayToolsSparseArraysExt.jl

@@ -18,4 +18,8 @@ function Base.copyto!(
     dest
 end
 
+# Fix for issue #486: Define issparse for AbstractVectorOfArray
+# AbstractVectorOfArray is not a sparse array type, so it should return false
+SparseArrays.issparse(::RecursiveArrayTools.AbstractVectorOfArray) = false
+
 end