remove __init__

[Oisin-M]

Description

Remove __init__.py from earthkit, and have all packages instead use earthkit-utils. This will allow import earthkit as ek; ek.subpkg to work regardless of the install method. Close #100.

Draft PR until eku is ready (and will need to pin eku version).

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

[Oisin-M]

Github action tests failing with a version issue (version file not being found), which I believe is caused by fetch-depth: 1 when checking out the repo. Locally the tests are passing for me

[Oisin-M]

Previous theory was incorrect. The issue was that git removes empty folders and this was causing the version file writing to fail