Require NegotiationResult to be Sendable

In NIOTypedApplicationProtocolNegotiationHandler<NegotiationResult> the
result is used to fulfil promises and perform hops so we need it to be
sendable when accessed from these other concurrency domains.

Sources/NIOTLS/NIOTypedApplicationProtocolNegotiationHandler.swift

@@ -39,9 +39,8 @@ import NIOCore
 /// specify a type that must be returned from the supplied closure. The result will then be used to succeed the ``NIOTypedApplicationProtocolNegotiationHandler/protocolNegotiationResult``
 /// promise. This allows us to construct pipelines that include protocol negotiation handlers and be able to bridge them into `NIOAsyncChannel`
 /// based bootstraps.
-public final class NIOTypedApplicationProtocolNegotiationHandler<NegotiationResult>: ChannelInboundHandler,
-    RemovableChannelHandler
-{
+@preconcurrency
+public final class NIOTypedApplicationProtocolNegotiationHandler<NegotiationResult: Sendable>: ChannelInboundHandler, RemovableChannelHandler {
     public typealias InboundIn = Any
 
     public typealias InboundOut = Any