Subpackages aren't getting packaged correctly

[deepyaman]

Description

From main (but also an issue in v0.1.0):

deepyaman@Deepyamans-MacBook-Pro leanframe % uv venv
Using CPython 3.13.4
Creating virtual environment at: .venv
Activate with: source .venv/bin/activate
deepyaman@Deepyamans-MacBook-Pro leanframe % source .venv/bin/activate
(leanframe) deepyaman@Deepyamans-MacBook-Pro leanframe % uv pip install 'leanframe @ git+https://github.com/tswast/leanframe'
Resolved 13 packages in 866ms
Prepared 1 package in 97ms
Installed 13 packages in 146ms
 + atpublic==7.0.0
 + ibis-framework==11.0.0
 + leanframe==0.1.0 (from git+https://github.com/tswast/leanframe@d8ce3677e5c6169b62cbbc5c10e8fd1ad61e1377)
 + numpy==2.4.4
 + pandas==3.0.2
 + parsy==2.2
 + pyarrow==23.0.1
 + python-dateutil==2.9.0.post0
 + six==1.17.0
 + sqlglot==30.2.1
 + toolz==1.1.0
 + typing-extensions==4.15.0
 + tzdata==2025.3
(leanframe) deepyaman@Deepyamans-MacBook-Pro leanframe % python
Python 3.13.4 (main, Jun  4 2025, 17:33:37) [Clang 20.1.4 ] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import leanframe
Traceback (most recent call last):
  File "<python-input-0>", line 1, in <module>
    import leanframe
  File "/Users/deepyaman/github/deepyaman/ibis-pandas/leanframe/.venv/lib/python3.13/site-packages/leanframe/__init__.py", line 17, in <module>
    from leanframe.core.session import Session
ModuleNotFoundError: No module named 'leanframe.core'
>>> 
(leanframe) deepyaman@Deepyamans-MacBook-Pro leanframe % ls -R /Users/deepyaman/github/deepyaman/ibis-pandas/leanframe/.venv/lib/python3.13/site-packages/leanframe 
__init__.py	__pycache__	version.py

/Users/deepyaman/github/deepyaman/ibis-pandas/leanframe/.venv/lib/python3.13/site-packages/leanframe/__pycache__:
__init__.cpython-313.pyc

Proposed solution

In https://deepyaman.substack.com/i/192903729/the-pandas-api-for-pandas, I worked around this by updating the pyproject.toml, but I also changed the build backend; not sure if you want to keep Setuptools.