Improve testing for StreamableHttpHandler and IdleTrackingBackgroundS… #97

Job	Run time
build (windows-latest, Debug)	4m 55s
build (macos-latest, Debug)	1m 8s
build (ubuntu-latest, Release)	2m 10s
build (windows-latest, Release)	5m 34s
build (ubuntu-latest, Debug)	2m 10s
build (macos-latest, Release)	1m 25s
publish-coverage / publish-coverage	31s
	17m 53s

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