[turbopack] Lazily construct `resolved::Requests` for `EsmAssetReference` (#83662)
Right now we construct `Request` objects eagerly when analyzing modules. This is on the critical path for analysis and can be expensive if there are a lot of exports (See [thread](https://vercel.slack.com/archives/C06PPGZ0FD3/p1757517287294729))
Instead just store the string and `parse` when resolving the reference. This should have identical caching semantics and by deferring the work we may be able to avoid it altogether if certain references never get resolved due to `sideEffects` configuration.