This spec sync updates the check transfers and entities surface.

• Check transfers: payer is now required when creating a check transfer (it was previously optional and defaulted to the return address). This breaks existing callers that omitted it.
• Check transfers: add return_address_name — a custom name printed above the Increase-managed return address (available both as a create param and on the physical-check response).
• Entities: add a validation_status filter (pending / valid / invalid) to the list endpoint.
• Minor generated documentation/serialization touch-ups (e.g. the pending-transaction amount description).

Note: making payer required is a breaking change for callers that previously omitted it.

Held for manual review — breaking change (payer became required) and an oversized diff (305 files) that is wildly out of line with the same sync in the other SDKs (~10–16 files). Not auto-merged; a human should verify the regeneration before merging.

Spec: 244db0c7a39ae8fff699dccda50b79bd.