Remove Cow around scalar buffers #1730

Job	Run time
build-benchmarks	2m 51s
Lint and Test	8m 19s
check-features-with-external-dependencies (-F gdal -F gdal/bindgen)	47s
check-features	17s
check-features-with-external-dependencies (-F geos)	19s
check-features (-F csv)	14s
check-features-with-external-dependencies (-F proj)	43s
check-features (-F flatgeobuf)	25s
check-features (-F flatgeobuf_async)	40s
check-features (-F geozero)	18s
check-features (-F ipc_compression)	41s
check-features (-F parquet)	16s
check-features (-F parquet_async)	23s
check-features (-F parquet_compression)	22s
check-features (-F polylabel)	14s
check-features (-F postgis)	33s
check-features (-F rayon)	15s
	17m 37s

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