Model effort values used by agent profiles and sessions.
@type t() :: :off | :minimal | :low | :medium | :high | :xhigh
@spec default() :: t()
@spec from_string(String.t()) :: {:ok, t()} | {:error, {:unknown_effort, String.t()}}
@spec label(t()) :: String.t()
@spec valid?(atom()) :: boolean()
@spec values() :: [t()]