Allow pool restarts on config change

Vitest will dispose of the pool and recreate it when the Vitest config
changes. This was causing `Miniflare` instances to be disposed, then
reused when the pool was recreated. This change moves the project
cache from the module-level to a "pool-level" local variable.

packages/vitest-pool-workers/src/pool/index.ts

@@ -613,6 +613,7 @@ function assertCompatibleVitestVersion(ctx: Vitest) {
 }
 
 export default function (ctx: Vitest): ProcessPool {
+	// This function is called when config changes and may be called on re-runs
 	assertCompatibleVitestVersion(ctx);
 
 	return {
@@ -767,13 +768,15 @@ export default function (ctx: Vitest): ProcessPool {
 			// thingModule.importers.add(testModule);
 		},
 		async close() {
+			// `close()` will be called when shutting down Vitest or updating config
 			log.debug("Shutting down runtimes...");
 			const promises: Promise<unknown>[] = [];
 			for (const project of allProjects.values()) {
 				if (project.mf !== undefined) {
 					promises.push(forEachMiniflare(project.mf, (mf) => mf.dispose()));
 				}
 			}
+			allProjects.clear();
 			await Promise.all(promises);
 		},
 	};