Refactor `js/storage/dmDb.js` to use a singleton connection pattern for IndexedDB.
Previously, the database was opened and closed for every single operation,
leading to significant overhead.
Changes:
- Introduced `dbInstance` and `dbPromise` to cache the database connection.
- Refactored `openDmDb` to reuse the existing connection or pending promise.
- Added `onversionchange` handler to safely close the connection if an upgrade is requested.
- Removed all manual `db.close()` calls from exported functions.
- Added a benchmark script in `tests/benchmark-dm-db.mjs` to verify the improvement.
Co-authored-by: PR0M3TH3AN <[email protected]>
- Added `db.close()` to exported functions in `js/storage/dmDb.js` to ensure IndexedDB connections are released.
- Patched `tests/test-helpers/setup-localstorage.mjs` to include a `structuredClone` polyfill required by `fake-indexeddb` in Node.js environments.
- Updated `tests/dm-normalization.test.mjs`, `tests/dm-db.test.mjs`, and `tests/nostr/dm-direct-message-flow.test.mjs` to conditionally initialize `fake-indexeddb` to prevent global conflicts.
- Verified fixes by running unit tests and the `scripts/agent/interop-test.mjs` E2E suite.
