Add ReduceOr (haven't yet added it to egglog!!!) #56

Job	Run time
test-linux (ubuntu-20.04, focal, clang-12, c++11)	12m 21s
test-linux (ubuntu-20.04, focal, clang-12, c++14)	11m 42s
test-linux (ubuntu-20.04, focal, clang-12, c++17)	11m 55s
test-linux (ubuntu-20.04, focal, clang-12, c++20)	12m 3s
test-linux (ubuntu-20.04, focal, gcc-11, c++11)	22m 9s
test-linux (ubuntu-20.04, focal, gcc-11, c++14)	10m 7s
test-linux (ubuntu-20.04, focal, gcc-11, c++17)	10m 1s
test-linux (ubuntu-20.04, focal, gcc-11, c++20)	10m 8s
test-linux (ubuntu-20.04, focal, clang-11, c++11)	12m 9s
test-linux (ubuntu-20.04, focal, gcc-10, c++11)	9m 49s
	2h 2m 24s

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