refactor(dm-db): use singleton IndexedDB connection to avoid N+1 overhead

Co-authored-by: PR0M3TH3AN <[email protected]>

benchmarks/dmDb-benchmark.mjs

@@ -0,0 +1,55 @@
+
+import { performance } from "perf_hooks";
+
+// Mock IndexedDB if running in Node
+if (!globalThis.indexedDB) {
+  const { indexedDB, IDBKeyRange } = await import("fake-indexeddb");
+  globalThis.indexedDB = indexedDB;
+  globalThis.IDBKeyRange = IDBKeyRange;
+}
+
+// Mock console to suppress logs
+const originalConsoleWarn = console.warn;
+console.warn = () => {};
+
+// Import after mocking console
+const { writeMessages, clearDmDb } = await import("../js/storage/dmDb.js");
+
+async function runBenchmark() {
+  await clearDmDb();
+
+  const iterations = 1000;
+  const messages = [];
+
+  for (let i = 0; i < iterations; i++) {
+    messages.push({
+      id: `msg-${i}`,
+      conversation_id: "conv-1",
+      sender_pubkey: "sender",
+      receiver_pubkey: "receiver",
+      created_at: Date.now(),
+      kind: 4,
+      content: `Message ${i}`,
+    });
+  }
+
+  console.log(`Starting benchmark with ${iterations} writes...`);
+
+  const start = performance.now();
+
+  // Simulate N+1 writes
+  for (const msg of messages) {
+    await writeMessages(msg);
+  }
+
+  const end = performance.now();
+  const duration = end - start;
+
+  console.log(`Total time: ${duration.toFixed(2)}ms`);
+  console.log(`Average time per write: ${(duration / iterations).toFixed(2)}ms`);
+
+  // Restore console
+  console.warn = originalConsoleWarn;
+}
+
+runBenchmark().catch(console.error);