Pinned vitest pool to forks in createVitestConfig (#27691)

no ref

This is a small adjustment for (what is currently) the posts, stats, and admin-x-settings. We've observed some occasional flakiness that seems to be from crossing boundaries, and moving to forks is going to be a slight perf hit but given this is what are otherwise-speedy unit tests with a limited app scope, it seems fine for now.

Switch the shared `createVitestConfig` from Vitest's default `threads`
pool to `forks`. Forks runs each worker as a separate child process,
giving stronger isolation than threads (which run in separate V8
isolates but still share the Node process — and therefore process-scoped
state).

Author: 9larsons

apps/admin-x-framework/src/test/vitest-config.ts

@@ -42,6 +42,10 @@ export function createVitestConfig(options: VitestConfigOptions = {}) {
         test: {
             globals: true,
             environment: 'jsdom',
+            // pool: 'forks' for process-level isolation in jsdom-heavy
+            // React suites; sidesteps Vitest threads-pool edge cases.
+            pool: 'forks',
+            isolate: true,
             setupFiles,
             include,
             silent,