[RFC]: Add anglit distribution implementation

### Description

This RFC proposes to add an implementation of the anglit probability distribution to stdlib, following existing continuous distribution patterns.

The anglit distribution has support on [-π/4, π/4] with PDF cos(2x), and is available in SciPy as scipy.stats.anglit.

References:
1. SciPy – https://docs.scipy.org/doc/scipy/reference/generated/scipy.stats.anglit.html

### Related Issues

Related issues # , # , and # .

### Questions

No.

### Other

No.

### Checklist

- [x] I have read and understood the [Code of Conduct](https://github.com/stdlib-js/stdlib/blob/develop/CODE_OF_CONDUCT.md).
- [x] Searched for existing issues and pull requests.
- [x] The issue name begins with `RFC:`.

未指定文件、测试或入口点。首先检查 stdlib 中现有的连续分布模式以及链接的 SciPy anglit 参考，然后确定项目预期的实现和验证约定。完成标准是添加一个 anglit 分布实现，支持 [-π/4, π/4]，且 PDF 为 cos(2x)。

由索引模型根据 Issue 内容生成。