Use more consistently int64 for page numbers in SLRU-related code

Use more consistently int64 for page numbers in SLRU-related code

clog.c, async.c and predicate.c included some SLRU page numbers still
handled as 4-byte integers, while int64 should be used for this purpose.

These holes have been introduced in 4ed8f0913bfd, that has introduced
the use of 8-byte integers for SLRU page numbers, still forgot about the
code paths updated by this commit.

Reported-by: Noah Misch
Author: Aleksander Alekseev, Michael Paquier
Discussion: https://postgr.es/m/20240626002747[email protected]
Backpatch-through: 17