fix HttpTransport to multiplex subscriptions over a single EventSource #517

Job	Run time
Server - linux-x86_64	16m 45s
Server - linux-aarch64	45m 26s
Desktop - Main x86_64-unknown-linux-gnu	29m 13s
Desktop - Main aarch64-apple-darwin	48m 23s
Desktop - Main x86_64-apple-darwin	53m 11s
Desktop - Main aarch64-unknown-linux-gnu	1h 4m 48s
Desktop - Main x86_64-pc-windows-msvc	32m 5s
Create Release	26s
	4h 50m 17s

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