[Python][Annotations] Should structure of annotations reflect structure of PyArrow at runtime

[rok]

Describe the enhancement requested

Currently proposed PyArrow annotations are stored in files to reflecting module names. PyArrow at runtime is structured slightly differently and the difference is adjusted for with annotation imports. As discussed here we should probably structure .pyi files such that they reflect the runtime structure of PyArrow.

Alternatively we could copy annotations into appropriately named files at wheel build time.

Component(s)

Python