Variable elimination reimplementation #985

Job	Run time
Julia 1 on ubuntu-latest (x64)	11m 20s
Julia 1 on macOS-latest (x64)	17m 20s
Julia 1 on windows-latest (x64)	14m 18s
Julia 1.9 on ubuntu-latest (x64)	21m 15s
Julia 1.9 on macOS-latest (x64)	21m 56s
Julia 1.9 on windows-latest (x64)	24m 24s
Julia nightly on ubuntu-latest (x64)	14m 7s
Julia nightly on macOS-latest (x64)	20m 7s
Julia nightly on windows-latest (x64)	19m 54s
	2h 44m 41s

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