feat: group a materialized view by GROUP BY (#4222)

A view could only map source rows one to one, or one to many through a
FROM-position item, so nothing could see all the rows sharing a key.

A view query now takes `GROUP BY expr, ...` with aggregate projections,
planned and executed by DataFusion over the lance scan. A group spans
fragments, so a grouped view is recomputed in full whenever its source
changes; each row's provenance is its group's smallest source row id.
Such a query is stored as definition format 2, so a reader that predates
grouping reports the view as unrefreshable instead of failing to parse
it.


Stacked on #4190.

nodejs/__test__/materialized_view.test.ts

@@ -54,7 +54,7 @@ describe("materialized views", () => {
 
     // A newer writer's layout is reported, never guessed at.
     for (const newer of [
-      `{"format":2,"query":${JSON.stringify(query)}}`,
+      `{"format":3,"query":${JSON.stringify(query)}}`,
       '{"kind":"select_v3","source_table":"people"}',
     ]) {
       expect(() => read(newer)).toThrow(/cannot refresh/);

nodejs/lancedb/materialized_view.ts

@@ -7,14 +7,17 @@ import { Table } from "./table";
 /** Schema metadata key holding a materialized view's definition. */
 export const DEFINITION_META_KEY = "mv.definition";
 
-/** The stored layout this version reads: `{"format": 1, "query": "<SQL>"}`. */
-export const DEFINITION_FORMAT = 1;
+/**
+ * The newest stored layout this version reads: `{"format": N, "query": "<SQL>"}`,
+ * format 2 being a query with `GROUP BY`.
+ */
+export const DEFINITION_FORMAT = 2;
 
 /**
  * The query that defines a materialized view, as stored:
  * `SELECT columns FROM [ns.]table [, function(args) AS alias | , UNNEST(column) AS alias]
- * [WHERE predicate] [LIMIT n]`. A Function in `FROM` position yields one row
- * per element it returns.
+ * [WHERE predicate] [GROUP BY expr, ...] [LIMIT n]`. A Function in `FROM`
+ * position yields one row per element it returns.
  */
 export interface MaterializedViewDefinition {
   /** The defining query, in the canonical spelling the server stores. */