v6 codemod: add await to convertToModelMessages calls

v6 codemod: add await to convertToModelMessages calls: a task in LegoFlow-SWE (Harbor dataset). convertToModelMessages (imported from 'ai' ) became async in AI SDK 6. Existing code that calls it without await will break at runtime. We need a codemod transformer that automatically adds await to…

The task

`convertToModelMessages` (imported from `'ai'`) became async in AI SDK 6. Existing code that calls it without `await` will break at runtime. We need a codemod transformer that automatically adds `await` to unawaited calls of this function, so that migration from v5 → v6 is seamless.

Part of Lego-X/LegoFlow-SWE.