fix(engine): expose session close #483

Job	Run time
Ensure the code builds (OoniStableFullRelease)	41s
Ensure the code builds (OoniStableFullRelease)	2m 22s
Ensure the code builds (OoniStableFdroidRelease)	49s
Ensure the code builds (OoniStableFdroidRelease)	2m 49s
Ensure the code builds (DwStableFullRelease)	58s
Ensure the code builds (DwStableFullRelease)	3m 10s
Ensure the code builds (DwStableFdroidRelease)	41s
Ensure the code builds (DwStableFdroidRelease)	3m 7s
Archive APKs	0s
Run unit tests	0s
Run unit tests	2m 30s
Run instrumented tests	0s
Upload artifact to Firebase App Distribution	0s
Upload artifact to Firebase App Distribution	49s
Run instrumented tests (25, default)	12m 11s
Archive APKs (OoniStableFullDebug)	2m 13s
Run instrumented tests (25, google_apis)	12m 17s
Archive APKs (OoniStableFdroidDebug)	2m 19s
Run instrumented tests (29, default)	12m 16s
Archive APKs (OoniDevFullDebug)	2m 14s
Run instrumented tests (29, google_apis)	12m 20s
Archive APKs (OoniDevFullDebugAndroidTest)	2m 8s
Archive APKs (DwStableFullDebug)	2m 18s
Archive APKs (DwStableFdroidDebug)	2m 8s
Archive APKs (DwDevFullDebug)	2m 16s
	1h 22m 36s

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