test(hygiene): close every brain the unit suite creates

Each file opened one or more Brainy instances (beforeEach, or a small
per-test helper like migration-gate-family-scoped's module-level seed())
and never closed them. migration-gate-family-scoped.test.ts now tracks
every brain seed() hands back in a describe-scoped array drained by
afterEach, since the helper itself lives outside the describe block.

tests/unit/utils/metadataIndex-array-bound.test.ts

@@ -48,6 +48,10 @@ describe('the indexable-array bound', () => {
     await brain.init()
   })
 
+  afterEach(async () => {
+    await brain.close()
+  })
+
   describe('BELOW the bound: the array indexes, every element of it', () => {
     it('the eleven-element array that used to vanish is searchable', async () => {
       // ELEVEN — one over the old silent limit, the whole shape of the defect.

tests/unit/utils/metadataIndex-sparse-range-collation.test.ts

@@ -42,7 +42,7 @@
  * column store adopts the field. It is named in `getIdsFromChunksForRange`'s
  * doc comment rather than papered over.
  */
-import { describe, it, expect, beforeEach } from 'vitest'
+import { describe, it, expect, beforeEach, afterEach } from 'vitest'
 import { Brainy } from '../../../src/brainy'
 import { NounType } from '../../../src/types/graphTypes'
 import { SparseIndex, ChunkManager } from '../../../src/utils/metadataIndexChunking'
@@ -122,6 +122,10 @@ describe('legacy sparse index: range queries order values, or refuse', () => {
     expect(index.columnStore.hasField(FIELD)).toBe(false)
   })
 
+  afterEach(async () => {
+    await brain.close()
+  })
+
   describe('(a) a long BOUND against ordinary short values', () => {
     // 'apple' < 'mango' < 'zebra', and every bound below is compared against
     // these three raw keys.