TST: Include __init__.py files in coverage report

Include `__init__.py` files in coverage report: the package's
`__init__.py` files contain code (e.g. the `data` module `load`
function)  that needs to be tested. If left outside coverage reports, no
awareness about their exercise exists, and bugs may go unnoticed.

Author: jhlegarreta

pyproject.toml

@@ -236,7 +236,6 @@ parallel = true
 concurrency = ["multiprocessing"]
 omit = [
   "^test/*",
-  "*/__init__.py",
   "*/conftest.py",
   "src/nifreeze/_version.py"
 ]