Replace event channel with broadcast channel #14365

Job	Run time
Build C library (ubuntu-latest)	20s
Build C library (macos-latest)	23s
cargo deny	30s
Rust doc comments	12s
Lint Rust	1m 10s
Check provider database	5s
Python lint	14s
Build deltachat-rpc-server (ubuntu-latest)	25s
Build deltachat-rpc-server (macos-latest)	30s
Build deltachat-rpc-server (windows-latest)	31s
Rust tests (ubuntu-latest, 1.77.1)	47s
Rust tests (windows-latest, 1.77.1)	32s
Rust tests (macos-latest, 1.77.1)	39s
Rust tests (ubuntu-latest, 1.77.0)	47s
JSON-RPC Python tests	0s
CFFI Python tests	0s
	7m 5s

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