Migrate the orchestrator to the `Buffer` abstraction as well. #805

Job	Run time
build_attest_all (buildconfigs/key_xor_test_app.sh)	41m 7s
build_attest_all (buildconfigs/oak_client_android_app.sh)	55m 15s
build_attest_all (buildconfigs/oak_containers_agent.sh)	35m 12s
build_attest_all (buildconfigs/oak_containers_kernel.sh)	33m 55s
build_attest_all (buildconfigs/oak_containers_orchestrator.sh)	50m 11s
build_attest_all (buildconfigs/oak_containers_stage1.sh)	48m 48s
build_attest_all (buildconfigs/oak_containers_syslogd.sh)	47m 6s
build_attest_all (buildconfigs/oak_containers_system_image.sh)	51m 40s
build_attest_all (buildconfigs/oak_containers_nvidia_system_image.sh)	52m 40s
build_attest_all (buildconfigs/oak_echo_enclave_app.sh)	41m 39s
build_attest_all (buildconfigs/oak_echo_raw_enclave_app.sh)	40m 43s
build_attest_all (buildconfigs/oak_functions_enclave_app.sh)	42m 49s
build_attest_all (buildconfigs/oak_functions_insecure_enclave_app.sh)	40m 54s
build_attest_all (buildconfigs/oak_orchestrator.sh)	41m 53s
build_attest_all (buildconfigs/oak_restricted_kernel_simple_io_init_rd_wrapper_bin.sh)	42m 41s
build_attest_all (buildconfigs/stage0_bin.sh)	58m 22s
build_attest_all (buildconfigs/stage0_bin_tdx.sh)	41m 22s
	12h 46m 17s

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