Add some clarifying comments to the forward_stream helper #734

Job	Run time
build_attest_all (buildconfigs/key_xor_test_app.sh)	19m 19s
build_attest_all (buildconfigs/oak_client_android_app.sh)	50m 2s
build_attest_all (buildconfigs/oak_containers_agent.sh)	11m 9s
build_attest_all (buildconfigs/oak_containers_kernel.sh)	34m 53s
build_attest_all (buildconfigs/oak_containers_orchestrator.sh)	24m 37s
build_attest_all (buildconfigs/oak_containers_stage1.sh)	25m 15s
build_attest_all (buildconfigs/oak_containers_syslogd.sh)	25m 38s
build_attest_all (buildconfigs/oak_containers_system_image.sh)	25m 24s
build_attest_all (buildconfigs/oak_containers_nvidia_system_image.sh)	27m 4s
build_attest_all (buildconfigs/oak_echo_enclave_app.sh)	19m 8s
build_attest_all (buildconfigs/oak_echo_raw_enclave_app.sh)	19m 53s
build_attest_all (buildconfigs/oak_functions_enclave_app.sh)	18m 52s
build_attest_all (buildconfigs/oak_functions_insecure_enclave_app.sh)	20m 1s
build_attest_all (buildconfigs/oak_orchestrator.sh)	20m 49s
build_attest_all (buildconfigs/oak_restricted_kernel_simple_io_init_rd_wrapper_bin.sh)	43m 23s
build_attest_all (buildconfigs/stage0_bin.sh)	47m 36s
build_attest_all (buildconfigs/stage0_bin_tdx.sh)	42m 13s
	7h 55m 16s

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