Restructuring quaddtype to use src layout

[SwayamInSync]

closes #252
As per the comment #252 (comment)

[SwayamInSync]

Following is the new quaddtype directory structure

├── LICENSE
├── README.md
├── docs
├── meson.build
├── pyproject.toml
├── reinstall.sh
├── src
│   ├── csrc
│   └── numpy_quaddtype
├── subprojects
└── tests
    ├── test_dot.py
    ├── test_finfo.py
    ├── test_multithreading.py
    ├── test_quaddtype.py
    └── utils.py

[juntyr]

LGTM

[ngoldbaum]

Sorry for the delay - I try not to spend too much time looking at code on weekends.

You should be on the lookout for any breakage that happens as a result of this.

Maybe also turn the docs build on for pull requests? I just checked and I don't think this break the docs build but it could have.

[SwayamInSync]

You should be on the lookout for any breakage that happens as a result of this.

As of now I didn't find any, meson nicely exposed the subproject's includes so they also don't need any change and workflows are also green.

Maybe also turn the docs build on for pull requests? I just checked and I don't think this break the docs build but it could have.

Right the current docs should be fine as it is very bare-minimum (all relying on autodoc extension)
I am working on a doc branch to add more content, there I'll also add the docs build on PR

[juntyr]

@SwayamInSync This still looks good to me, I'd be happy with you merging it

[SwayamInSync]

Waiting for the #246 get resolved first as this restructuring might cause confusion there :)