Sync 3 diffs to facebookresearch/optimizers

[wz337]

Summary:
Syncs the internal dev tree to the OSS mirror (fbcode/ai_codesign/optimizers) via
scripts/oss_sync.sh. Changes included since the last sync marker:

• [shampoo] Newton-Schulz inverse root (D115751122)
• [pyre][automated] Remove unused type error suppressions - hpc (D116361970)
• [shampoo][dev] Fix OSS mypy on ShampooPT2CompileConfig's synthesized base class
  (D116658375, stacked below this diff)

Most of this diff is machine output; two files are not. The mirrored .py files under
distributed_shampoo/ and gpa/ are regenerated by the script. CHANGELOG.md and
distributed_shampoo/__init__.py were edited by hand — details below. Every bullet in the
new ## 2026-08-19 entry was hand-written: the generator emits
<commit title> — <first line of the Summary: section>, which for these three commits
produced a link preamble, internal tooling narration, and a sentence truncated mid-clause.
See D116693368 for the before/after and the rewrite rules. Two bullets in the generated set
were dropped rather than rewritten:

• The cast(torch.Tensor, param) mypy fix (D113741320) already shipped to the mirror in the
  2026-07-31 sync; it reappeared only because that sync left the marker short. Its code is
  not in this diff.
• The pyre suppression sweep reduces to nothing an OSS reader can act on once the internal
  tool name is removed.

distributed_shampoo/__init__.py is the one mirror .py file oss_sync.sh does not
regenerate (it is manually maintained, by design). NewtonSchulzRootInvConfig was missing
from it while the release note advertises the feature, so it is added to the imports and
__all__ alongside its sibling RootInvConfig subclasses.

Also advances the non-exported last-sync marker at scripts/.last_oss_sync_rev to
efefb9b4 (D115751122) — the newest landed dev-path commit at sync time. Note this does
not cover D116658375, which was uncommitted when the notes ran but whose change is in
this mirror. The next sync will therefore re-list it; drop that duplicate bullet then, or
re-run with an explicit --since.

Differential Revision: D116658374

[meta-codesync]

@wz337 has exported this pull request. If you are a Meta employee, you can view the originating Diff in D116658374.