perf: Improve `median` with no grouping by 2X (#14399) #13

Job	Run time
cargo test hash collisions (amd64)	23m 32s
linux build test	4m 48s
Run sqllogictests with the sqlite test suite	1h 5m 45s
cargo test 'extended_tests' (amd64)	18m 45s
	1h 52m 50s

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