nodejs_compat selects Node.js compat v2 once compatibility_date is 2024-09-23 or later

Before compatibility date 2024-09-23 the nodejs_compat flag provided a small hand-written subset of Node.js APIs, and the fuller polyfill set required the separate nodejs_compat_v2 flag. From 2024-09-23 onward nodejs_compat alone selects v2 behaviour, which adds node: module aliasing, globals such as Buffer and process, and support for importing built-ins that libraries expect to exist.

The usual failure mode is a project pinned to an older compatibility date that pulls in a library expecting Buffer to be global, and gets Buffer is not defined at runtime rather than at build time. The fix is to move compatibility_date past 2024-09-23 and keep only nodejs_compat in compatibility_flags, dropping nodejs_compat_v2, which is redundant at that date. Bumping the date changes other runtime semantics too, so run the test suite after.