fix(ext/kv): add missing getMany method (#18410)

The `getMany` method was missing from the implementation of the
`Deno.Kv` class. This patch fixes it.

cli/tests/unit/kv_test.ts

@@ -548,6 +548,16 @@ async function setupData(db: Deno.Kv) {
     .commit();
 }
 
+dbTest("get many", async (db) => {
+  await setupData(db);
+  const entries = await db.getMany([["b", "a"], ["a"], ["c"]]);
+  assertEquals(entries, [
+    { key: ["b", "a"], value: 100, versionstamp: "00000000000000010000" },
+    { key: ["a"], value: -1, versionstamp: "00000000000000010000" },
+    { key: ["c"], value: null, versionstamp: null },
+  ]);
+});
+
 dbTest("list prefix", async (db) => {
   await setupData(db);
   const entries = await collect(db.list({ prefix: ["a"] }));

ext/kv/01_db.ts

@@ -72,6 +72,36 @@ class Kv {
     return deserializeValue(entries[0]);
   }
 
+  async getMany(
+    keys: Deno.KvKey[],
+    opts?: { consistency?: Deno.KvConsistencyLevel },
+  ): Promise<Deno.KvEntry[]> {
+    keys = keys.map(convertKey);
+    const ranges: RawKvEntry[][] = await core.opAsync(
+      "op_kv_snapshot_read",
+      this.#rid,
+      keys.map((key) => [
+        null,
+        key,
+        null,
+        1,
+        false,
+        null,
+      ]),
+      opts?.consistency ?? "strong",
+    );
+    return ranges.map((entries, i) => {
+      if (!entries.length) {
+        return {
+          key: keys[i],
+          value: null,
+          versionstamp: null,
+        };
+      }
+      return deserializeValue(entries[0]);
+    });
+  }
+
   async set(key: Deno.KvKey, value: unknown) {
     key = convertKey(key);
     value = serializeValue(value);