feat: MemRDD — in-memory database engine (Go map-based)
Complete in-memory RDD implementation:
- CRUD: Create, Append, GetValue, PutValue, Delete, Recall
- Navigation: GoTo, GoTop, GoBottom, Skip, BOF, EOF
- Index: CreateIndex (sorted slice + binary search), Seek (exact + soft)
- Bulk: Pack (remove deleted), Zap (clear all)
- Multi-open: shared table across work areas
- Driver registered as "MEMRDD", prefix "mem:"
Tests: 9 tests including 5000-record stress test
Create, Append/Get/Put, Navigation, Delete/Pack, Zap,
Index (string + numeric), Seek (exact + soft), Stress 5000, Multi-open
Use cases: temp tables, query results, pivot, caching
Performance: no disk I/O, no byte packing — pure Go slices
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>