test(hygiene): close every brain the remaining suites create

id-normalization.test.ts's makeBrain() and degraded-reads-surfaced.test.ts's
per-test brains had nothing tracking them — both now use a describe-scoped
opened[] array drained by afterEach.

find-hybrid-filter-before-hydrate.test.ts had two beforeAll-built brains
(one per describe block) with no matching afterAll.

multi-process-safety.test.ts and plugin-autodetect.test.ts/plugin.test.ts
left a brain whose init() was expected to reject (a rejected init() still
registers the instance in Brainy's global instance registry — the
constructor does that unconditionally — so it still needs close() to
deregister, or the process-level shutdown hooks never see the registry go
idle for the rest of the run).

tests/unit/plugin.test.ts

@@ -298,9 +298,10 @@ describe('Brainy plugin integration', () => {
     // must surface as a failed init(), NOT a silent degrade to the default
     // engine (the version-coupling guard; see plugin-version-coupling.test.ts).
     await expect(brain.init()).rejects.toThrow(/failed to activate|native module not found/)
+    await brain.close().catch(() => {})
   })
 
-  it('should use() return this for chaining', () => {
+  it('should use() return this for chaining', async () => {
     const plugin: BrainyPlugin = {
       name: 'chain-test',
       activate: async () => true
@@ -309,5 +310,8 @@ describe('Brainy plugin integration', () => {
     const brain = new Brainy({ requireSubtype: false, storage: { type: 'memory' } })
     const result = brain.use(plugin)
     expect(result).toBe(brain)
+    // Never init()'d — the constructor still registered it in Brainy's global
+    // instance registry, so it still needs a close() to deregister.
+    await brain.close().catch(() => {})
   })
 })