fix(useLocalStorage): return null after explicit removal instead of initialValue

[DISCONECTED-png]

Problem

Calling setValue(null) correctly removes the item from localStorage,
but the hook returns initialValue instead of null after removal.

Steps to reproduce:
const [value, setValue] = useLocalStorage('key', 'default');
setValue(null);
// Expected: value === null
// Actual: value === 'default'

Root Causes

Two issues working against each other:

1. Return value fallback — store ? JSON.parse(store) : initialValue
   treats a missing key as "never initialized" with no way to distinguish
   it from an intentional removal.

2. Effect re-seeds storage — the useEffect runs after setState(null)
   (because removing the item triggers a re-render) and immediately writes
   initialValue back into storage, undoing the removal entirely.

Fix

Added a wasRemovedRef to track when the item is explicitly cleared.

• The useEffect now skips re-seeding when wasRemovedRef.current is true
• The return value resolves to null instead of initialValue in that case
• The ref resets when key changes (new key = fresh initialization)

Same fix applies to useSessionStorage which shares the same pattern.

Fixes #344