Various improvements to `POSet` #3680

Job	Run time
Version Sync	9s
Nix flake (self-hosted, linux, normal)	4m 3s
Nix flake (macos-13, macos-13)	3m 49s
Nix flake (MacM1, self-macos-12)	4m 0s
Check Java code formatting	20s
K Tests	2m 59s
K Ubuntu Jammy Package	3m 14s
Performace Tests	1s
	18m 35s

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