Add scheduling, machine info, caching strategies and devices (#9)

Reviewed-on: Rubydragon/MetagraphOptimization.jl#9
Co-authored-by: Anton Reinhard <anton.reinhard@proton.me>
Co-committed-by: Anton Reinhard <anton.reinhard@proton.me>

src/graph/validate.jl

@@ -59,3 +59,19 @@ function is_valid(graph::DAG)
 
     return true
 end
+
+"""
+    is_scheduled(graph::DAG)
+
+Validate that the entire graph has been scheduled, i.e., every [`ComputeTaskNode`](@ref) has its `.device` set.
+"""
+function is_scheduled(graph::DAG)
+    for node in graph.nodes
+        if (node isa DataTaskNode)
+            continue
+        end
+        @assert !ismissing(node.device)
+    end
+
+    return true
+end