Various improvements to `POSet` #3692

Job	Run time
Nix flake (self-hosted, linux, normal)	7m 53s
Version Sync	6s
Nix flake (macos-13, macos-13)	14m 43s
Nix flake (MacM1, self-macos-12)	23m 44s
Check Java code formatting	26s
K Tests	51m 25s
K Ubuntu Jammy Package	29m 33s
Performace Tests	11m 0s
	2h 18m 50s

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