[Spanify] Add tests for partition alloc

This commit introduces a tests specific to PartitionAlloc spanification
efforts.

This change is the second step towards enabling spanification for PartitionAlloc
and other third-party libraries. These projects require specific configurations,
such as different header paths for `base::span` or custom exclusion logic,
which will be handled based on the selected project.

The default behavior remains targeted at Chrome (`--project=chrome`).

Design doc: go/partition-alloc-spanification

Change-Id: I3062ad54632e6bbd1ed2f74add4bc5fb753da135
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7552499
Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Reviewed-by: Stephen Nusko <nuskos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1592292}
NOKEYCHECK=True
GitOrigin-RevId: a6bc171e7d0c065831dc77c56491de29cb52d1ac