src: lib: hub: Send a burst of initial heartbeats if needed #142

Job	Run time
test	4m 27s
build (macos-latest, aarch64-apple-darwin)	13m 13s
build (macos-latest, x86_64-apple-darwin)	12m 51s
build (ubuntu-latest, arm-unknown-linux-musleabihf)	7m 7s
build (ubuntu-latest, aarch64-unknown-linux-musl)	6m 44s
build (ubuntu-latest, armv7-unknown-linux-musleabihf)	6m 38s
build (ubuntu-latest, x86_64-unknown-linux-musl)	6m 23s
build (windows-latest, x86_64-pc-windows-msvc, .exe)	17m 32s
	1h 14m 55s

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