add bulk_init_chunk_size in torchrec (#2638) #9596

Job	Run time
build_test (linux.2xlarge, 3.10, py310) / linux-job	2m 53s
build_test (linux.2xlarge, 3.11, py311) / linux-job	2m 47s
build_test (linux.2xlarge, 3.12, py312) / linux-job	3m 45s
build_test (linux.2xlarge, 3.9, py39) / linux-job	2m 33s
	11m 58s

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