fix(vue): eslint/tsconfig migration + resolve type errors

@robonen/vue (toolkit): migrate to eslint flat config + composite tsconfig;
fix composable + test type errors (writable computed returns, null guards,
overload-compatible signatures, typed test helpers) — all type-level.

vue/toolkit/src/composables/reactivity/index.ts

@@ -1,4 +1,22 @@
 export * from './broadcastedRef';
+export * from './refAutoReset';
+export * from './refDebounced';
+export * from './refThrottled';
+export * from './until';
+export * from './useArrayFilter';
+export * from './useArrayFind';
+export * from './useArrayMap';
 export * from './useCached';
+export * from './useCloned';
+export * from './useCycleList';
 export * from './useLastChanged';
+export * from './usePrevious';
 export * from './useSyncRefs';
+export * from './useToNumber';
+export * from './useToString';
+export * from './watchDebounced';
+export * from './watchIgnorable';
+export * from './watchOnce';
+export * from './watchPausable';
+export * from './watchThrottled';
+export * from './whenever';