Deduplicate decimal128 conversion #13515

Job	Run time
checks / other-checks	51s
checks / check-style	3m 8s
devcontainer / build (amd64, 12.2, conda)	5m 0s
devcontainer / build (amd64, 12.2, pip)	4m 56s
static-configure	0s
conda-cpp-build	0s
wheel-build-cudf	0s
conda-cpp-tests	0s
conda-python-build	0s
conda-cpp-checks	0s
conda-java-tests	0s
wheel-build-cudf-polars	0s
wheel-tests-cudf	0s
pandas-tests	0s
unit-tests-cudf-pandas	0s
wheel-build-dask-cudf	0s
conda-python-cudf-tests	0s
conda-notebook-tests	0s
conda-python-other-tests	0s
docs-build	0s
wheel-tests-cudf-polars	0s
pandas-tests-diff	0s
wheel-tests-dask-cudf	0s
pr-builder	1s
	13m 56s

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