serde_json::Value is pretty large, and is contributing (albeit not
exclusively) to the large size of the Value repr. Putting it in a box
is *especially* cheap (since it's rarely used) and allows us
to (eventually) cut down on the size of Value.
Change-Id: I005a802d8527b639beb4e938e3320b11ffa1ef23
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10795
Reviewed-by: sterni <sternenseemann@systemli.org>
Autosubmit: aspen <root@gws.fyi>
Tested-by: BuildkiteCI