[DOCS] showcases, examples & general docs improvements

:mega: THIS IS A CALL FOR DOCS
Feel free to add pull requests with examples here:
- https://github.com/CycloneDX/cyclonedx-python-lib/tree/main/examples
- https://github.com/CycloneDX/cyclonedx-python-lib/blob/main/docs/examples.rst

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There are currently no (complex) examples how to use this lib.

Yes, there are API docs, and small snippets, but no examples.
Even the unit tests do now showcase example usage, as they are much declarative or not expressive enough.

GOAL:
- [x] have examples in a `examples` folder
- [x] link the examples in the README
- [x] link the examples in the (api)-docs
- [x] prevent `examples` dir from being shipped (sdist/bdist)
- [x] have examples run in CI

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首先检查现有的 examples/ 目录和 docs/examples.rst，然后查看它们是如何从 README 和 API 文档链接的。由于列出的每个目标都会经过检查，请先确定示例或文档中仍存在的缺口；完成的标准是记录一个有用的复杂用法示例，并确保相关链接和 CI 预期保持正确。

由索引模型根据 Issue 内容生成。