[Feature Request]: Materialized views (CREATE MATERIALIZED VIEW)

**Version:** `8.0.30-MatrixOne-v3.0.11` (MatrixOne v3.0.11)

Regular views work, but `CREATE MATERIALIZED VIEW` is rejected, so there is no built-in way to maintain incremental pre-aggregated rollups.

**Reproduce**
```sql
CREATE VIEW v AS SELECT u, count(*) c FROM s GROUP BY u; -- OK
CREATE MATERIALIZED VIEW mv AS SELECT u, count(*) c FROM s GROUP BY u; -- SQL parser error
```

**Request**
Support materialized views (incrementally maintained) for rollups / dashboards.

---
_Found while evaluating MatrixOne git4data / SQL as a data-versioning & agent-trace backend. Version: `8.0.30-MatrixOne-v3.0.11` (MatrixOne v3.0.11)._

## Testing background
Found in the same observability work: we wanted **incrementally maintained pre-aggregated rollups** (error-rate / latency per service) that update as new spans arrive, instead of rescanning raw spans for every dashboard refresh. Regular `CREATE VIEW` works; `CREATE MATERIALIZED VIEW` does not.

## Why it matters (expected purpose)
Materialized (incrementally maintained) views let dashboards and alerts read cheap pre-aggregates over a high-volume firehose. This is a common pattern in trace/metrics backends and is currently missing.