vgsp: fail4 r224 alias witnesses - OUT-ALIAS-WIT / IN-ALIAS-WIT + pre/post csumHEADmaster

r224 evidence: the failing outputs ARE produced by the engine and read back
byte-identical (OUT-PAGE-WIT vs sema-bigcopy src16 match exactly), but the
engine's result is structurally corrupted: for every gemm of the tested
chains the row band >= 16 (the by>=1 CTA band) replicates a single tile per
output buffer (Q band=[0,-7.96875], K band=[7.96875,7.96875], ...) while the
first pages carry the correct/partial values; the corruption starts exactly
at the row-16 boundary. The pre/post csum pair proves each 'changed' page
was really rewritten by the engine (bounce != copy-in baseline), so the
replicated band is engine-authored, not pass-through.

Add the two witnesses that name the replication source in the next cycle:

- OUT-ALIAS-WIT: each changed page's first 8 bytes matched against the
  earlier changed pages of the same launch -> logs (va, bi) partner pairs.
- IN-ALIAS-WIT: consecutive copy-in recs with identical content (equal
  per-page csum) -> a replicated INPUT region (one page served for many
  VAs, e.g. an X/weight buffer) is caught before any launch runs.
- OUT-PAGE-WIT extended with pre/post csum.

All bounded, behind the existing gsp_phys_gr_copyout_dump gate, and using
the established single-inflight static scratch discipline.

(cherry picked from commit 7c9d48847cffa2a21263515b94bdb57ad2a9357c)

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