Combine Publisher share replace once

Publisher+shareReplayOnce.swift

public extension Publisher {

    /// A variation on [share()](https://developer.apple.com/documentation/combine/publisher/3204754-share)
    /// that allows for buffering and replaying a single event to future subscribers.
    ///
    /// - Parameter initialValue: The initial value of the buffer, if none has been emitted before.
    /// - Returns: A publisher that replays the event to future subscribers.
    func shareReplayOnce(initialValue: Output) -> Publishers.Autoconnect<Publishers.Multicast<Self, CurrentValueSubject<Output, Failure>>> {
        multicast { CurrentValueSubject(initialValue) }
            .autoconnect()
    }

    /// A variation on [share()](https://developer.apple.com/documentation/combine/publisher/3204754-share)
    /// that allows for buffering and replaying a single event to future subscribers.
    ///
    /// - Returns: A publisher that replays the event to future subscribers.
    func shareReplayOnce() -> AnyPublisher<Output, Failure> {
        map(Optional.some)
            .shareReplay(initialValue: .none)
            .compactMap { $0 }
            .eraseToAnyPublisher()
    }

}