This was pointed out by Daywalker [1]: we are synchronously processing
events from `lightningd` which means that if processing one of the
hooks or requests was slow or delayed, we would not get notifications,
hooks, or RPC requests, massively impacting the flexbility.
This highlights the issue with a failing test (it times out), and in
the next commit we will isolate event processing into their own task,
so to free the event loop from having to wait for an eventual
response.
[1] https://community.corelightning.org/c/developers/hold-invoice-plugin#comment_wrapper_16754493
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