test: allow more time for large model bridge encoding

Give the 600 KiB request encoding round-trip test 15 seconds instead of the default 5 seconds after a CI timeout. Preserve the payload size, all assertions, global test timeout, and production behavior.

Validation: all nine model bridge contract tests and file-scoped ESLint passed. The full typecheck/lint command was cancelled before its completion could be confirmed.

src/shared/model-bridge-contracts.test.ts

@@ -116,7 +116,7 @@ describe('model bridge contracts and codec', () => {
     expect(left).toEqual(right)
     expect(left.byteLength).toBeGreaterThan(600 * 1024)
     await expect(decodeModelBridgeMessage(left)).resolves.toEqual(message)
-  })
+  }, 15_000)
 
   it('round trips response, error, and delivery ACK messages', async () => {
     const requestDigest = await digestModelBridgeRequest(request)