fix: MATCH ... CREATE ... RETURN creates once per row (GQLITE-T-0488) - #200

Summary

• MATCH (a) CREATE (a)-[:T]->(:New) RETURN a created one node, not one per row, and the RETURN rows included the new node. MATCH (a:Missing) CREATE (:New) RETURN count(*) created a node. Also in v0.12.0.
• Cause: the MATCH+CREATE+RETURN handler's fallback ran MATCH+CREATE, then the MATCH again for the RETURN. The fallback now runs in the row pipeline (GQLITE-T-0488).
• known.json: the GQLITE-T-0488 entry is removed.

Test plan

• tests/functional/106_create_per_row_return.sql
• Unit 1030/1030; functional; TCK 3880/3880 on SQLite 3.53 and 3.54.1; Python 1669 passed.
• Metamorphic: cover reps 2 and random seeds 1, 50001, 90001 (20000 each): 0 new signatures; no write_return mismatch left.

Semantic coverage matrix

• tests/functional/106 covers CREATE per row with RETURN, an aggregate RETURN, and a MATCH with no rows.

Checklist

• Tests added
• No version bump