`Publishers.FlatMap` should request `.unlimited` demand instead of `.max(1)` if itself received unlimited demand. Failing test case here: https://github.com/cx-org/CombineX/blob/master/Tests/CXInconsistentTests/FailingTests/FailingFlatMapSpec.swift
Publishers.FlatMapshould request.unlimiteddemand instead of.max(1)if itself received unlimited demand.Failing test case here: https://github.com/cx-org/CombineX/blob/master/Tests/CXInconsistentTests/FailingTests/FailingFlatMapSpec.swift