Build project and adapt package exports

[ScriptedAlchemy]

## Description

This PR adapts the `runtime-core` package to use Rslib's default file naming conventions for its build output.

Key changes include:
*   **Updated `package.json` exports**: `main`, `module`, `exports`, and `types` fields are now correctly configured to reference the default `.js`, `.cjs`, and `.d.ts` files generated by Rslib in the `dist` directory.
*   **Enabled Declaration File Generation**: Configured `runtime-core` to correctly generate and reference TypeScript declaration files (`.d.ts`).
*   **Resolved Build Errors**: Fixed a `TS1192` error in the `runtime` package by correcting an incorrect default import from `runtime-core`.

These changes ensure the `runtime-core` package builds successfully with standard Rslib output and has correctly configured package exports for consumers.

## Related Issue

<!--- This project only accepts pull requests related to open issues -->
<!--- If suggesting a new feature or change, please discuss it in an issue first -->
<!--- If fixing a bug, there should be an issue describing it with steps to reproduce -->
<!--- Please link to the issue here: -->


## Types of changes

- [ ] Docs change / refactoring / dependency upgrade
- [x] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)

## Checklist

- [ ] I have added tests to cover my changes.
- [ ] All new and existing tests passed.
- [ ] I have updated the documentation.