Client router should discard stale prefetch entries for static pages (#79309)
When navigating to a static page that was previously prefetched, the
client router should discard a stale prefetch entry, and fetch the page
again, if the stale time has passed.
The selected stale time is either the default value of 5 minutes, a
custom value set via `experimental.staleTimes.static`, or a stale value
set via a `cacheLife` profile when using `"use cache"`.
This also fixes an issue where the client router interpreted the stale
time value as milliseconds, whereas the server sends it in seconds. This
was previously already fixed with `clientSegmentCache` enabled in
#74759.
fixes #74272
fixes #79093
Closes NEXT-4109