Spanification of partition_alloc/pointers/raw_ptr_unittest.cc

This is the result of running the automatic spanification on linux and
updating code to use and pass spans where size is known.

The original patch was fully automated using script:
//tools/clang/spanify/rewrite-multiple-platforms.sh -platforms=linux
Then refined with gemini-cli and at last manually refined

Gemini-CLI auto-fixes for compilation

Bug: 501143531
Change-Id: Ib8a48320e8a6b7e3db0b02412bd708d94a85696f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7834126
Reviewed-by: Stephen Nusko <nuskos@chromium.org>
Commit-Queue: Daniel Angulo <angdaniel@google.com>
Cr-Commit-Position: refs/heads/main@{#1696422}