pt: add explicit decay_rate for lr #6531

Job	Run time
Build source distribution	16s
determine-arm64-runner	1s
Build wheels for cp311-manylinux_x86_64	6m 34s
Build wheels for cp311-manylinux_x86_64	6m 37s
Build wheels for cp311-macosx_x86_64	7m 0s
Build wheels for cp311-macosx_arm64	3m 42s
Build wheels for cp311-win_amd64	8m 10s
Build wheels for cp310-manylinux_aarch64	5m 35s
build_pypi_index	10s
build_docker (12)	10m 28s
upload_pypi	0s
build_docker (_cu11, 11)	4m 8s
deploy_pypi_index	0s
Pass testing build wheels	3s
	52m 44s

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