Per feedback_no_htod_htoh_only_mapped_pinned: mapped-pinned only for
CPU↔GPU; tests not exempt. Previous commit ab64c0412 was a shallow
deprecated-API swap (memcpy_stod -> clone_htod) — both still HTOD
copies. This commit replaces all 5 uploads and the 1 readback in
test_eval_action_select_thompson_picks_proportionally with the
production mapped-pinned + memcpy_dtod_async pattern (mirrors lines
433-448 of the same file).
Closure 'upload_pinned' DRYs the 5 upload sites; readback uses
MappedI32Buffer + DtoD into staging.host_slice_mut().to_vec().
Zero HTOD/HTOH copies remain in this file. Documented in
dqn-wire-up-audit.md.
8d72c14a8b