Improve CostHashAgg with single-column NDV and spill-aware cost model #970

Job	Run time
check-skip	3s
Build Apache Cloudberry DEB	14m 58s
prepare-test-matrix-deb	3s
DEB Install Test Apache Cloudberry	2m 15s
ic-cbdb-parallel	29m 7s
ic-deb-good-opt-off	25m 53s
pax-ic-deb-good-opt-on	26m 58s
gpcontrib-gp-stats-collector	3m 11s
pax-ic-deb-good-opt-off	22m 15s
ic-deb-good-opt-on	27m 37s
ic-deb-contrib	3m 36s
ic-deb-gpcontrib	4m 28s
Generate Apache Cloudberry Build Report	3s
	2h 40m 27s

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