[PyROOT] Move CPython extensions in subdirectories

[guitargeek]

Closes https://github.com/root-project/root/issues/14917.

To backport to 6.32 for making the packagers happy with our new release.

[github-actions[bot]]

Test Results

    13 files      13 suites   2d 16h 17m 3s :stopwatch:  3 024 tests  2 659 :white_check_mark: 0 :zzz: 365 :x: 33 795 runs  33 019 :white_check_mark: 0 :zzz: 776 :x:

For more details on these failures, see this check.

Results for commit 760027a1.

:recycle: This comment has been updated with latest results.

[dpiparo]

I am re-running all tests since we had some failures a while ago.