Aggregating metrics causes crash in membrane_core

Logs below originate from the FishJam tests, problem was reported by @Rados13
%Membrane.ParentError{
  message: "Error starting child :endpoint_bin, reason: {%Membrane.ParentError{message: \"Error starting child :ice, reason: {:badarg, [{:ets, :insert, [#Reference<0.2241832208.2648571908.247683>, {{:message_queue_length, [\\\"<0.3072.0>/\\\", \\\"{:endpoint, \\\\\\\"b07d2473-354a-452f-9f43-489912be630c\\\\\\\"}/\\\", \\\":endpoint_bin/\\\", \\\":ice\\\"], nil}, {:__membrane_stalker_function_metric__, #Function<2.21975877/0 in Membrane.Core.Element.init/1>}}], [error_info: %{cause: :id, module: :erl_stdlib_errors}]}, {Membrane.Core.Element, :init, 1, [file: ~c\\\"lib/membrane/core/element.ex\\\", line: 119]}, {:gen_server, :init_it, 2, [file: ~c\\\"gen_server.erl\\\", line: 980]}, {:gen_server, :init_it, 6, [file: ~c\\\"gen_server.erl\\\", line: 935]}, {:proc_lib, :init_p_do_apply, 3, [file: ~c\\\"proc_lib.erl\\\", line: 241]}]}\"}, [{Membrane.Core.Parent.ChildLifeController.StartupUtils, :start_child, 6, [file: ~c\"lib/membrane/core/parent/child_life_controller/startup_utils.ex\", line: 230]}, {Enum, :\"-map/2-lists^map/1-1-\", 2, [file: ~c\"lib/enum.ex\", line: 1700]}, {Membrane.Core.Parent.ChildLifeController, :setup_children, 3, [file: ~c\"lib/membrane/core/parent/child_life_controller.ex\", line: 253]}, {Enum, :\"-flat_map_reduce/3-fun-1-\", 3, [file: ~c\"lib/enum.ex\", line: 1301]}, {Enumerable.List, :reduce, 3, [file: ~c\"lib/enum.ex\", line: 4842]}, {Enum, :flat_map_reduce, 3, [file: ~c\"lib/enum.ex\", line: 1300]}, {Membrane.Core.Parent.ChildLifeController, :handle_spec, 2, [file: ~c\"lib/membrane/core/parent/child_life_controller.ex\", line: 141]}, {Membrane.Core.CallbackHandler, :\"-handle_callback_result/5-fun-0-\", 5, [file: ~c\"lib/membrane/core/callback_handler.ex\", line: 196]}, {Enum, :\"-reduce/3-lists^foldl/2-0-\", 3, [file: ~c\"lib/enum.ex\", line: 2528]}, {Membrane.Core.CallbackHandler, :handle_callback_result, 5, [file: ~c\"lib/membrane/core/callback_handler.ex\", line: 194]}, {Membrane.Core.Bin, :init, 1, [file: ~c\"lib/membrane/core/bin.ex\", line: 134]}, {:gen_server, :init_it, 2, [file: ~c\"gen_server.erl\", line: 980]}, {:gen_server, :init_it, 6, [file: ~c\"gen_server.erl\", line: 935]}, {:proc_lib, :init_p_do_apply, 3, [file: ~c\"proc_lib.erl\", line: 241]}]}"
}
    (membrane_core 1.1.0-rc0) lib/membrane/core/parent/child_life_controller/startup_utils.ex:230: Membrane.Core.Parent.ChildLifeController.StartupUtils.start_child/6
    (elixir 1.16.0) lib/enum.ex:1700: Enum."-map/2-lists^map/1-1-"/2
    (membrane_core 1.1.0-rc0) lib/membrane/core/parent/child_life_controller.ex:253: Membrane.Core.Parent.ChildLifeController.setup_children/3
    (elixir 1.16.0) lib/enum.ex:1301: anonymous fn/3 in Enum.flat_map_reduce/3
    (elixir 1.16.0) lib/enum.ex:4842: Enumerable.List.reduce/3
    (elixir 1.16.0) lib/enum.ex:1300: Enum.flat_map_reduce/3
    (membrane_core 1.1.0-rc0) lib/membrane/core/parent/child_life_controller.ex:141: Membrane.Core.Parent.ChildLifeController.handle_spec/2
    (membrane_core 1.1.0-rc0) lib/membrane/core/callback_handler.ex:196: anonymous fn/5 in Membrane.Core.CallbackHandler.handle_callback_result/5
    (elixir 1.16.0) lib/enum.ex:2528: Enum."-reduce/3-lists^foldl/2-0-"/3
    (membrane_core 1.1.0-rc0) lib/membrane/core/callback_handler.ex:194: Membrane.Core.CallbackHandler.handle_callback_result/5
    (membrane_core 1.1.0-rc0) lib/membrane/core/bin.ex:134: Membrane.Core.Bin.init/1
    (stdlib 5.2) gen_server.erl:980: :gen_server.init_it/2
    (stdlib 5.2) gen_server.erl:935: :gen_server.init_it/6
    (stdlib 5.2) proc_lib.erl:241: :proc_lib.init_p_do_apply/3
membraneframework / membrane_core

Aggregating metrics causes crash in membrane_core #814
