Look up one vulnerability by its identifier

Defined for the cybersecurity databank. The entity here is the vulnerability, so this is the entry point for a caller that holds an identifier rather than a package it is running -- every other route requires a package name. Returns the affected package and range, the version that fixes it, severity, and exploitation status. Fields are returned as claims carrying their own authority: status 'known' with authority 'exclusive' means Daystruct has evidence for the value, while status 'unknown' with authority 'non_exclusive' means Daystruct has no evidence either way and the answer does not contradict or supersede what the caller already knows. Exploitation is never reported as false, because the known-exploited catalog held here is a partial slice.