The remaining optimisation for `V1Lazy` for a listener
in the negotiation, whereby the listener delays flushing
of the multistream version header, is hereby removed.
The remaining effect of `V1Lazy` is only on the side of
the dialer, which delays flushing of its singular
protocol proposal in order to send it together with
the first application data (or an attempt is made to
read from the negotiated stream, which similarly
triggers a flush of the protocol proposal). This
permits `V1Lazy` dialers to be interoperable with
`V1` listeners. The remaining theoretical pitfall whereby
application data gets misinterpreted as another protocol
proposal by a listener remains, however unlikely.

`V1` remains the default, but we may eventually risk
just making this lazy dialer flush a part of the default
`V1` implementation, removing the dedicated `V1Lazy`
version identifier.

Every multistream-select version maps to a specific header line,
but there may be different variants of the same multistream-select
version using the same header line, i.e. the same wire protocol.