fix: prevent race condition and panic in events.Producer.Broadcast

[Lil-Duckling-22]

Fix race condition in events.Producer.Broadcast that caused panics when subscriptions were cancelled concurrently with broadcasts. Copy subscription list under lock and add recover() to handle closed channel panics.

Without this fix, the application crashes with "send on closed channel" panic when Next() closes a subscription channel while Broadcast sends to it.

[CLAassistant]

All committers have signed the CLA.

[rauljordan]

This PR has a fundamental problem. Consider the following:

1. You copy subs under read lock
2. You release the lock
3. A subscription could be cancelled and its channel closed in Start()
4. Your goroutines then try to send on the closed channel, causing a panic
   the panic recovery is hiding a fundamental design flaw, and I think this PR doesn't introduce any improvements that are noteworthy unfortunately. We will have to close