Context

This is a proof of concept to improve kernel facilities when testing in lib_scoru_wasm (following comments from @ovidiudeac (!6428 (comment 1116461979), !6428 (comment 1116461986)) and @lthms (!6428 (comment 1116311722))

It improves the testing in two parts:

kernels are no longer filename but directly a lazily read kernel. I've made the choice to make it lazy to avoid reading ALL the kernels at the startup of the tests, but still read them only once (especially unreachable that is used extensively).
instrument test_with_kernel to actually return an Alcotest test. Instead of a plain string for the test name, it takes a format of type (string -> string, unit, string) format to print the used kernel nicely, for example: "Testing %s kernel before being stuck".

Manually testing the MR

dune exec src/lib_scoru_wasm/test/test_scoru_wasm.exe

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