GetNewX25519Cert, GetNewmldsa65 and GetNewmlkem768 parsed xray's stdout by
reading lines[0], lines[1] and each line's second colon-separated field
without any length check — unlike GetNewEchCert, which already guards its
line count. If the xray binary printed fewer than two lines or reformatted
its labels (a version change, or a silent failure that emitted nothing),
the fixed slice index panicked and the handler 500'd.
Extract the shared parsing into parseXrayKeyPairOutput, which length guards
the line count and each label split and returns an error instead of
panicking, then route all three generators through it.
MHSanaei