When dynamicIO is enabled, missing data is encoded to an infinitely hanging promise, the absence of which we use to determine if a segment is fully static or partially static. However, when dynamicIO is not enabled, this trick doesn't work.

Previously, if PPR is enabled, and dynamicIO is not, we were conservative and assumed that all segments are partial. That doesn't need to be the case, though. We can use the `onPostpone` callback of the `prerender` function to determine if a given RSC node is partial.

To make sure that this works as expected, we're disabling `dynamicIO` in `test/e2e/app-dir/segment-cache/incremental-opt-in`.

Without this change, the following tests would fail because additional requests for the PPR-enabled routes are triggered when `dynamicIO` is disabled:

- `when a link is prefetched with <Link prefetch=true>, no dynamic request is made on navigation`
- `when prefetching with prefetch=true, refetches cache entries that only contain partial data`
- `when prefetching with prefetch=true, refetches partial cache entries even if there's already a pending PPR request`

In addition, we're also disabling `dynamicIO` in `test/e2e/app-dir/segment-cache/client-only-opt-in` as well as
`test/e2e/app-dir/segment-cache/export`, to prepare for an upcoming change where `ppr` will be enabled automatically when `dynamicIO` is enabled. Those three tests are then not compatible with `dynamicIO` because they either rely on the `'incremental'` PPR config, or on `output: 'export'`.

To prepare for an upcoming change where `ppr` will be enabled automatically when `dynamicIO` is enabled, we're disabling `dynamicIO` in the global default cache handler test, and using the `useCache` config instead, because `output: 'standalone'` is currently not compatible with PPR.

To prepare for an upcoming change where `ppr` will be enabled
automatically when `dynamicIO` is enabled, we're hard coding `ppr: true`
in the Dynamic IO tests with this PR. The non-PPR assertions are
subsequently removed, which makes up most of the changed lines.

We can now also exclude the tests in the PPR tests manifest, so that
they're not run twice in CI.

> [!NOTE]  
> This PR is best reviewed with hidden whitespace changes.