Parallelize decryption of reports #5626

Job	Run time
Additional Builds and Concurrency Tests	14m 59s
Measure coverage	28m 54s
Basic Checks	19m 46s
miri	3m 5s
Release builds and tests	8m 27s
sanitize (address)	18m 23s
Slow tests	17m 31s
sanitize (address, multi-threading)	19m 36s
sanitize (leak)	7m 50s
sanitize (leak, multi-threading)	8m 29s
	2h 27m 0s

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