rework async request handling #1070

Job	Run time
static analysis (Elixir 1.15.x \| Erlang/OTP 25.x)	31s
mix test windows (Elixir 1.13.x \| Erlang/OTP 22.x)	9m 9s
mix test (Elixir 1.13.x \| Erlang/OTP 22.x)	6m 16s
mix test (Elixir 1.13.x \| Erlang/OTP 23.x)	7m 3s
mix test (Elixir 1.13.x \| Erlang/OTP 24.x)	4m 37s
mix test windows (Elixir 1.13.x \| Erlang/OTP 23.x)	10m 8s
mix test (Elixir 1.13.x \| Erlang/OTP 25.x)	1m 45s
mix test windows (Elixir 1.13.x \| Erlang/OTP 24.x)	7m 22s
mix test (Elixir 1.14.x \| Erlang/OTP 23.x)	6m 28s
mix test windows (Elixir 1.13.x \| Erlang/OTP 25.x)	6m 44s
mix test (Elixir 1.14.x \| Erlang/OTP 24.x)	1m 40s
mix test windows (Elixir 1.14.x \| Erlang/OTP 23.x)	9m 49s
mix test (Elixir 1.14.x \| Erlang/OTP 25.x)	4m 39s
mix test windows (Elixir 1.14.x \| Erlang/OTP 24.x)	8m 13s
mix test (Elixir 1.15.x \| Erlang/OTP 24.x)	1m 36s
mix test windows (Elixir 1.14.x \| Erlang/OTP 25.x)	6m 56s
mix test (Elixir 1.15.x \| Erlang/OTP 25.x)	1m 31s
mix test windows (Elixir 1.15.x \| Erlang/OTP 24.x)	8m 3s
mix test windows (Elixir 1.15.x \| Erlang/OTP 25.x)	6m 45s
	1h 49m 15s

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