spg-storage 7.8.0

In-memory storage primitives for SPG: values, rows, table schema, catalog with foreign-key constraints.
Documentation

In-memory storage primitives.

v0.3 is intentionally simple: a flat catalog of tables, each holding rows as Vec<Value> (positional, matching the table's TableSchema). No MVCC, no on-disk format — those land in later milestones.