make apply_mask a bit more efficient #62

Job	Run time
build_artifact (x86, linux.4xlarge, default, 3.10, clang)	7m 36s
build_artifact (x86, linux.4xlarge, default, 3.9, clang)	7m 30s
build_artifact (x86, linux.4xlarge, default, 3.11, gcc)	7m 34s
build_artifact (x86, linux.4xlarge, default, 3.11, clang)	7m 31s
build_artifact (x86, linux.4xlarge, default, 3.9, gcc)	7m 31s
build_artifact (x86, linux.4xlarge, default, 3.10, gcc)	7m 31s
build_artifact (x86, linux.4xlarge, default, 3.12, gcc)	7m 29s
build_artifact (arm, linux.arm64.m7g.4xlarge, default, 3.11, gcc)	8m 19s
build_artifact (x86, linux.4xlarge, default, 3.13, gcc)	7m 20s
build_artifact (arm, linux.arm64.m7g.4xlarge, default, 3.9, clang)	8m 25s
build_artifact (x86, linux.4xlarge, default, 3.13, clang)	7m 28s
build_artifact (arm, linux.arm64.m7g.4xlarge, default, 3.12, clang)	8m 27s
build_artifact (arm, linux.arm64.m7g.4xlarge, default, 3.9, gcc)	8m 31s
build_artifact (arm, linux.arm64.m7g.4xlarge, default, 3.11, clang)	8m 41s
build_artifact (arm, linux.arm64.m7g.4xlarge, default, 3.10, gcc)	8m 22s
build_artifact (arm, linux.arm64.m7g.4xlarge, default, 3.10, clang)	8m 41s
build_artifact (arm, linux.arm64.m7g.4xlarge, default, 3.12, gcc)	8m 36s
build_artifact (x86, linux.4xlarge, default, 3.12, clang)	7m 30s
build_artifact (arm, linux.arm64.m7g.4xlarge, default, 3.13, clang)	8m 28s
build_artifact (arm, linux.arm64.m7g.4xlarge, default, 3.13, gcc)	8m 31s
torchrec_cpu_tests	1s
	2h 40m 2s

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