Use compare_by_identity hash for the map in Circuit. This fixes…

… a bug

that appeared with newer Ruby versions where people would use
`GC.verify_compaction_references` to optimize memory consumption. After using
the compaction, the circuit map would be corrupted when a task was a `Method`
reference, leading to the following exception.
NoMethodError: undefined method `[]' for nil
     /home/nick/projects/trailblazer-activity/lib/trailblazer/activity/circuit.rb:80:in `next_for'
thanks to @tiagotex for deep-diving into Ruby to find where this originates from
and also providing a simple solution. :wine:

lib/trailblazer/activity/schema/compiler.rb

@@ -24,7 +24,7 @@ def call(intermediate, implementation, config_merge: {})
 
           # From the intermediate "template" and the actual implementation, compile a {Circuit} instance.
           def schema_components(intermediate, implementation, config)
-            wiring = {}
+            wiring = {}.compare_by_identity # https://ruby-doc.org/3.3.0/Hash.html#class-Hash-label-Modifying+an+Active+Hash+Key
             nodes_attributes  = []
 
             intermediate.wiring.each do |task_ref, outs|

test/activity_test.rb

@@ -87,3 +87,41 @@ def call(*)
     assert_equal activity.extend(call_module).call, "overridden call!"
   end
 end
+
+class GCBugTest < Minitest::Spec
+  it "still finds {.method} tasks after GC compression" do
+    intermediate = Activity::Schema::Intermediate.new(
+      {
+        Activity::Schema::Intermediate::TaskRef(:a) => [Activity::Schema::Intermediate::Out(:success, :b)],
+        Activity::Schema::Intermediate::TaskRef(:b, stop_event: true) => []
+      },
+      {:b => :success},
+      :a # start
+    )
+
+    module Step
+      extend T.def_tasks(:create)
+    end
+
+    implementation = {
+      :a => Schema::Implementation::Task(Step.method(:create), [Activity::Output(Activity::Right, :success)], []),
+      :b => Schema::Implementation::Task(Trailblazer::Activity::End.new(semantic: :success), [], []),
+    }
+
+
+    activity = Activity.new(Activity::Schema::Intermediate::Compiler.(intermediate, implementation))
+
+    assert_invoke activity, seq: %([:create])
+
+# TODO: add tests for different Rubys
+    GC.verify_compaction_references(expand_heap: true, toward: :empty)
+
+# Without the fix, this *might* throw the following exception:
+#
+# NoMethodError: undefined method `[]' for nil
+#     /home/nick/projects/trailblazer-activity/lib/trailblazer/activity/circuit.rb:80:in `next_for'
+
+    assert_invoke activity, seq: %([:create])
+  end
+
+end