overwrite `field` data with `computedFields` values

When defining a document with a `field` and `computedFields` child item with the same name, the `computedFields` field seems to be appended onto the generated type. Resulting in undesired types for the field.

I would have expected the `computedFields` data to overwrite the `field` data, both the `description` and the `type`.

For reference, I am converting a comma separated string of `tags` into a parsed array via the `computedFields`. Here is an example of my document definition:

```js
export const Blog = defineDocumentType(() => ({
name: "Blog",
filePathPattern: `blog/**/*.md`,
fields: {
tags: {
type: "string",
description: "Comma separated listing of tags",
required: false,
},
},
computedFields: {
tags: {
description: "new description",
type: "list",
of: { type: "string" },
resolve: (item) =>
item?.tags?.split(",")?.map((tag) => tag.trim()) ?? undefined,
},
},
}));
```

Generates these types (simplified for the example):

```ts
/** Document types */
export type Blog = {
/** Comma separated listing of tags */
tags?: string | undefined
/** new description */
tags: list
}
```

Extra note: It also seems like the `computedFields` children do not support `list` types, or it may be a bug?

该 issue 未指定源文件或测试；从 Blog defineDocumentType 重现开始，跟踪字段和 computedFields 如何变成生成的类型。验证计算字段是否会替换原始描述和类型，以及是否支持列表类型。完成标准是生成的类型包含预期的单个 tags 字段，并为此示例提供回归测试覆盖。

由索引模型根据 Issue 内容生成。