Align hx-sse events with hx-multipart & hx-ws

[scriptogre]

Aligns SSE message hooks with the other streaming extensions.

// htmx:sse:before:message
{ message, cancelled, waitUntil }

// htmx:sse:after:message
{ message }

Adds:

• waitUntil(promise) to delay processing
• cancelled = true or preventDefault() to skips the message

PR #3960 separately adds connection to event detail.