Reduce default Vitest batch size to 5, enforce single-threaded execution, and refactor unit test wait conditions:

- Adjusted `run-vitest-unit-batches.mjs` to lower default batch size from 10 to 5 and enforce single-threaded execution for more predictable test behavior.
- Updated GitHub workflows to align with new batch size defaults.
- Introduced `waitForCondition` helper in unit tests to replace arbitrary delays with predicate-based waiting.
- Refactored `useEdgeGatewayTerminal` for improved session handling, including idle delay for shell polling and cleanup of request queuing logic.

.github/workflows/tests.yml

@@ -55,7 +55,7 @@ jobs:
       - name: Unit tests
         run: npm run test:unit
         env:
-          VITEST_BATCH_SIZE: 10
+          VITEST_BATCH_SIZE: 5
 
   e2e-smoke:
     if: github.event_name != 'schedule'