CVE-2024-32648: vyper default functions don't respect nonreentrancy keys

Prior to v0.3.0, __default__() functions did not respect the @nonreentrancy decorator and the lock was not emitted. This is a known bug and was already visible in the issue tracker (https://github.com/vyperlang/vyper/issues/2455), but it is being re-issued as an advisory so that tools relying on the advisory publication list can incorporate it into their searches.

A contract search was additionally performed and no vulnerable contracts were found in production.