add primitives for Thomas' spake2 #1039

Job	Run time
Tests with OCaml 5 (5.2.1, ubuntu-latest)	1m 22s
Tests with OCaml 5 (5.2.1, macos-latest)	2m 0s
Tests (4.14.2, ubuntu-latest)	2m 0s
Tests (4.14.2, macos-latest)	3m 42s
	9m 4s

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