Keep EventSource alive until all subscriptions are closed

[ranile]

Update EventSourceSubscription to hold an Rc<EventSource> to prevent premature closure of the EventSource.

While I would've preferred to hold a &EventSource in EventSourceSubscription, that would force EventSourceSubscription to not be 'static, which is needed for spawn_locals and borrows would make lifetimes a nightmare to deal with

fixes #495

[ranile]

I really don't like that this is possible at compile time but I don't see another way to fix the bigger issue of silent EventSource closures without lifetime pains

[Madoshakalaka]

Solid changes. However, dropping an EventSource no longer closes the connection or notifies subscribers. Users who relied on drop(es) (or letting es go out of scope) to signal teardown to subscribers now need to call es.close() instead.

This is a behavioral breaking change even though the API surface is nearly identical. It should be called out in a CHANGELOG entry, something like:

Breaking: EventSource no longer closes the underlying connection on drop. The connection now stays alive as long as any EventSourceSubscription exists. Call EventSource::close() to shut down immediately.

[ranile]

This is a behavioral breaking change even though the API surface is nearly identical. It should be called out in a CHANGELOG entry, something like:

Breaking: EventSource no longer closes the underlying connection on drop. The connection now stays alive as long as any EventSourceSubscription exists. Call EventSource::close() to shut down immediately.

Done. The root version is not updated in the CHANGELOG as that is done by another PR

[Madoshakalaka]

Looking good!