Fixed stale fetch using when page regenerates (#58926)
fixes: #58909
x-ref: #58321, #56472, #56231
Removed the Math.round of age since it can cause stale fetch data to be
considered not stale if the age rounds downwards. (5.49 is rounded to 5)
Note: This most likely also fixes some bugs with
revalidateTag/revalidatePath. Tested some tag/path issues that got fixed
with this change.
I think this is because revalidatetag/path sets [data.revalidatedAt =
Date.now()](https://github.com/vercel/next.js/blob/canary/packages/next/src/server/lib/incremental-cache/file-system-cache.ts#L120)
for file-system-cache. And with the current code that value would
continue to be "not stale" for up to 0.499 ms.
Co-authored-by: JJ Kasper <jj@jjsweb.site>
Co-authored-by: Zack Tanner <zacktanner@gmail.com>
