Switch to src layout, move tests to root

[effigies]

Closes #147.

Also, somehow, closes #131. See #131 (comment).

$ du -sh dist/*         
12K	dist/lazy_loader-0.5rc0.dev0-py3-none-any.whl
16K	dist/lazy_loader-0.5rc0.dev0.tar.gz
$ tar -tf dist/*.tar.gz
lazy_loader-0.5rc0.dev0/
lazy_loader-0.5rc0.dev0/CHANGELOG.md
lazy_loader-0.5rc0.dev0/LICENSE.md
lazy_loader-0.5rc0.dev0/MANIFEST.in
lazy_loader-0.5rc0.dev0/PKG-INFO
lazy_loader-0.5rc0.dev0/README.md
lazy_loader-0.5rc0.dev0/pyproject.toml
lazy_loader-0.5rc0.dev0/setup.cfg
lazy_loader-0.5rc0.dev0/src/
lazy_loader-0.5rc0.dev0/src/lazy_loader/
lazy_loader-0.5rc0.dev0/src/lazy_loader/__init__.py
lazy_loader-0.5rc0.dev0/src/lazy_loader.egg-info/
lazy_loader-0.5rc0.dev0/src/lazy_loader.egg-info/PKG-INFO
lazy_loader-0.5rc0.dev0/src/lazy_loader.egg-info/SOURCES.txt
lazy_loader-0.5rc0.dev0/src/lazy_loader.egg-info/dependency_links.txt
lazy_loader-0.5rc0.dev0/src/lazy_loader.egg-info/requires.txt
lazy_loader-0.5rc0.dev0/src/lazy_loader.egg-info/top_level.txt
lazy_loader-0.5rc0.dev0/tests/
lazy_loader-0.5rc0.dev0/tests/__init__.py
lazy_loader-0.5rc0.dev0/tests/fake_pkg/
lazy_loader-0.5rc0.dev0/tests/fake_pkg/__init__.py
lazy_loader-0.5rc0.dev0/tests/fake_pkg/__init__.pyi
lazy_loader-0.5rc0.dev0/tests/fake_pkg/some_func.py
lazy_loader-0.5rc0.dev0/tests/import_np_parallel.py
lazy_loader-0.5rc0.dev0/tests/test_lazy_loader.py
$ unzip -l dist/*.whl
Archive:  dist/lazy_loader-0.5rc0.dev0-py3-none-any.whl
  Length      Date    Time    Name
---------  ---------- -----   ----
    10909  05-17-2025 13:57   lazy_loader/__init__.py
     1539  05-17-2025 13:57   lazy_loader-0.5rc0.dev0.dist-info/licenses/LICENSE.md
     7515  05-17-2025 13:57   lazy_loader-0.5rc0.dev0.dist-info/METADATA
       91  05-17-2025 13:57   lazy_loader-0.5rc0.dev0.dist-info/WHEEL
       12  05-17-2025 13:57   lazy_loader-0.5rc0.dev0.dist-info/top_level.txt
      529  05-17-2025 13:57   lazy_loader-0.5rc0.dev0.dist-info/RECORD
---------                     -------
    20595                     6 files

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.27%. Comparing base (024e49f) to head (79aa9d0).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #151      +/-   ##
==========================================
- Coverage   96.00%   87.27%   -8.73%     
==========================================
  Files           5        1       -4     
  Lines         250      110     -140     
  Branches        0       20      +20     
==========================================
- Hits          240       96     -144     
+ Misses         10        7       -3     
- Partials        0        7       +7     

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[stefanv]

Thanks, @effigies! src layout isn't common in the SP ecosystem, but I don't feel strongly about it. Not sure I follow why this closes #131 🤷‍♂️