IndexedDB Plugin

### Clear and concise description of the problem

Have an indexed plugin to help build offline apps with less boilerplate

### Suggested solution

```ts
const plugin = createIndexedDBPlugin({
// ...
})
```

### Alternative

_No response_

### Additional context

_No response_

### Validations

- [x] Follow our [Code of Conduct](https://github.com/Akryum/rstore/blob/main/CODE_OF_CONDUCT.md)
- [x] Read the [Contributing Guidelines](https://github.com/Akryum/rstore/blob/main/CONTRIBUTING.md).
- [x] Read the [docs](https://rstore.starpad.dev/guide/).
- [x] Check that there isn't [already an issue](https://github.com/Akryum/rstore/issues) that requests the same feature to avoid creating a duplicate.

Begin by reviewing the project guide and the proposed createIndexedDBPlugin entry point to understand the existing store and plugin conventions. The issue does not name implementation files, tests, or a defined API; the work is complete only when a decided IndexedDB plugin supports the stated offline-app goal and its behavior is validated.

Written by the indexing model from the issue text.