fix(storage-reverse-image-search): stop native tfjs addon breaking tests in CI

[cabljac]

Fixes #355.

Problem

storage-reverse-image-search:test fails intermittently in CI with:

The Node.js native addon module (tfjs_binding.node) can not be found ...

Suites fail to load (not fail assertions), which bails the lerna test run. Same class of bug as firestore-semantic-search.

Root cause

1. Most suites transitively import src/common/feature_vectors.ts, which does import * as tf from '@tensorflow/tfjs-node'.
2. @tensorflow/tfjs-node loads a platform-specific native addon at import time.
3. CI installs with npm ci --ignore-scripts, so tfjs-node's postinstall that downloads the addon never runs. The addon is absent.
4. Whether a run passed depended on whatever node_modules was restored from the Lerna cache, so it passed/failed at random - and only in CI.

Fix - split unit and integration tests

• Unit run (default test script): maps @tensorflow/tfjs-node to a lightweight stub via moduleNameMapper. The many suites that mock feature_vectors or never invoke it stop crashing at import time.
• Integration run (npm run test:integration via jest.integration.config.js): the two specs that genuinely exercise TensorFlow - feature_vectors.test.ts and feature_vectors.memory.test.ts, which load a real model over the network and assert on real tensors/memory - move here. They need the native addon built and network access, so they do not belong in the --ignore-scripts CI job. They are preserved, not deleted.

The stub lives outside a __mocks__ directory on purpose: manual mocks for node_modules packages are auto-applied by jest and cannot be disabled per-config, which would also break the integration run. Wiring it through moduleNameMapper keeps it scoped to the unit config.

Verification

Reproduced the CI failure locally by removing the native addon: 10 suites failed to load. With the fix applied and the addon still absent, the unit run (against the Firestore emulator) is green: 15 suites pass, 0 failures. The integration config resolves the real tfjs package.

Companion to the same fix for firestore-semantic-search (#1106).

[cabljac]

Consolidating both tfjs test fixes into #1106. The two extensions must be fixed on the same branch for CI to pass (lerna nx-bail stops at the first failing extension), so this change is folded into that PR. #355 tracked there.