Add backpressure control and allow asynchronous flushing #155

Job	Run time
Build Unity package	0s
Build Libraries / Build Native library (osx-arm64)	7m 51s
Build Libraries / Build Native library (linux-x64)	3m 17s
Build Libraries / Build Native library (osx-x64)	6m 34s
Build Libraries / Build Native library (win-arm64)	3m 29s
Build Libraries / Build Native library (win-arm64-uwp)	3m 0s
Build Libraries / Build Native library (win-x64)	8m 5s
Build Libraries / Build Native library (android-arm)	1m 9s
Build Libraries / Build Native library (android-arm64)	1m 11s
Build Libraries / Build Native library (android-x64)	1m 15s
Build Libraries / Build Native library (ios-arm64)	41s
Build Libraries / Build Native library (ios-x64)	43s
Build Libraries / Build and pack .NET library	1m 11s
Build Libraries / Update pre-built libraries for Unity	0s
	38m 26s

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