We assumed page was loaded because before inserting we would move there. `NewRowId` unfortunately moves cursor to the rightmost page causing eviction of root page -- this arose the issue with `insert_into_page` not loading the page we were supposed to have loaded so I added `return_if_locked_maybe_load` which is a utility macro to check if the page is locked and if not, load it if needed.
Since page cache is now shared by default, we need to cache pages by
page number and something else. I chose to go with max_frame of
connection, because this connection will have a max_frame set until from
the start of a transaction until the end of it.
With key pairs of (pgno, max_frame) we make sure each connection is
caching based on the snapshot it is at as two different connections
might have the same pageno being using but a different frame. If both
have same max_frame then they will share same page.
