Add author_ror_display_names to FeatureBlock signatures Arrow contract

[atalyaalon]

What

Adds author_ror_display_names to the FeatureBlock signatures Arrow contract: a per-signature list<string> of ROR-normalized affiliation names. Threaded through FeatureBlockSignature (optional, defaults to empty) and to_arrow_tables. No feature consumes it yet — this makes it a recognized wire field so the scholar producer can populate it ahead of a future affiliation-normalization feature. Version bump 0.51.1 → 0.51.2 (manifests/lockfiles synced).

Part of the Arrow wire-bundle work

• Base incremental Arrow API: [codex] add direct Arrow incremental prediction #78
• Producer (scholar): allenai/scholar#41984
• Consumer (s2ads): allenai/s2-author-disambiguation-service#87
• Tracking issue: allenai/scholar#42050

Backward compatible: existing producers that omit the column read as empty (s2and ignores unknown columns; the field defaults to ()).