Introduce nightly build for incremental but full recipe coverage

This is to discuss a feature to implement in order to have a full recipe coverage build time.
The idea is to compile every nights a subset of our recipes.
```
name: Nightly build
on:
schedule:
- cron: '0 2 * * *' # run at 2 AM UTC

jobs:
nightly:
name: Nightly build
...
```
This covers builds time checks first and may cover runtime checks in the future.

先从提议的 GitHub Actions 工作流及其 nightly 调度开始，然后确定应如何将 recipes 划分为 nightly 子集。完成的标准是：nightly build 随时间推移编译每个 recipe，并提供构建时覆盖率检查；运行时检查留待未来工作。

由索引模型根据 Issue 内容生成。