memprove run exit codes

Exit	Meaning
the command’s own code (128 + N for signal N)	the command ran and its result was recorded
125	the command could not be started (recorded as UNAVAILABLE), its result could not be recorded, or no token was found (nothing ran; standard error names the places looked at); standard error says which
2	usage error: an ID that is neither given nor in the context, a control character in the program or an argument, a token-shaped string in the argv, a --test-cases value that is not a count

With --test-format cargo the case count is the passed plus failed tests summed over every test result: line; with --test-format pytest it is the passed plus failed plus error cases of the summary on the last line, else the marks of a progress line ((counted from the progress line)); output that cannot be read either way records no count, and such a run never passes.

From docs/guide.md at 2625064cbf0a · Markdown