refactor(pkgs): share vitest config and dedupe helpers (#3384)

tsconfigs/vitest.base.mts

@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+export default {
+	resolve: {tsconfigPaths: true},
+	test: {
+		globals: true,
+		environment: 'node',
+		include: ['**/*.{test,spec}.{ts,tsx}'],
+		exclude: ['node_modules', 'dist'],
+		coverage: {
+			provider: 'v8',
+			reporter: ['text', 'json', 'html'],
+			exclude: ['**/*.test.tsx', '**/*.spec.tsx', 'node_modules/'],
+		},
+	},
+};