CVE-2024-24563: Vyper negative array index bounds checks

Arrays can be keyed by a signed integer, while they are defined for unsigned integers only. The typechecker doesn’t throw when spotting the usage of an int as an index for an array. Typically, negative integers are filtered out at runtime by the bounds checker, but small enough (i.e. large in magnitude, ex. -2**255 + 5) quantities combined with large enough arrays (at least 2**255 in length) can pass the bounds checker, resulting in unexpected behavior.

A contract search was performed, and no production contracts were found to be impacted.