Dynamic import tracking should never be applied to edge runtime code,
because:
1. `dynamicIO` prerendering is not supported for edge
2. the implementation of `dynamicIO` prerendering relies on
node-specific APIs.

I missed this in #74152. This PR fixes a couple things:
- We no longer apply the dynamic import tracking to any edge modules
- Just to be safe, `trackDynamicImport` and `new CacheSignal` will now
throw if it's called from the edge runtime
- However, if `track-module-loading` does end up in an edge module, we
don't want to error at the top-level when creating
`moduleLoadingSignal`, so it is now initialized lazily. This is a bit
ugly, but `AppRouteRouteModule` currently pulls all prerendering-related
code in at the top level (instead of e.g. a conditional `require()` when
prerendering), so it *is* included in edge route handlers, even if
unused.
- this also required changing `__next_require__`/`__next_chunk_load__`
to only track module loading in DIO prerenders, otherwise we'd attempt
to create `moduleLoadingSignal` in edge RSC too

I also fixed a potential unhandled rejection in `CacheSignal.trackRead`,
because `.finally` rejects even if the original error was caught
somewhere else. (thanks for finding this one @gnoff!)