Feat: add "definePackageConfig" and "defineRootConfig" to make type definition closer to actual work

### Description

current, defineConfig type definition allow to write root only option(e.g. run.enablePrePostScripts) to package. but actually, it does not works. this problem is not good of developer experience.

### Suggested solution

Add "definePackageConfig" and "defineRootConfig" function. this will be exported by "vite-plus". "defineRootConfig" is just alias of "defineConfig" but "definePackageConfig" has new type definition.

### code example

```typescript
// workspace/packages/main/vite.config.ts
// this is package's config file.
import { definePackageConfig } from "vite-plus"

export default definePackageConfig({
run: {
enablePrePostScripts:true // happen type error because run.enablePrePostScripts is root only option
}
})
```

```typescript
// workspace/vite.config.ts
// this is root's config.
import { defineRootConfig } from "vite-plus"

export default defineRootConfig({
run: {
enablePrePostScripts:true // does not happen type error.
}
})
```

also, this is just coding rules. no one can stop to use "defineConfig" or "defineRootConfig" in package's vite.config.ts.
this proposal make "defineConfig" deprecated and recommend use new function.

### Alternative

Add more readable jsdoc e.g. "@root-only - this option does not work on package's config". but probably, developer will fail to notice.

### Additional context

_No response_

### Validations

- [x] Read the [Contributing Guidelines](https://github.com/voidzero-dev/vite-plus/blob/main/CONTRIBUTING.md).
- [x] Confirm this request is for Vite+ itself and not for Vite, Vitest, tsdown, Rolldown, or Oxc.
- [x] Check that there isn't already an issue requesting the same feature.

Start by locating the existing defineConfig type definition and the vite-plus export entry point. Trace how root and package configuration types are represented, then verify that defineRootConfig accepts root-only options while definePackageConfig rejects them; also check the proposed deprecation guidance for defineConfig.

Scritto dal modello di indicizzazione a partire dal testo della issue.