pyproject.toml: Install package in src/

[tomtseng]

Changes

Bug:

-> uv run python
Python 3.12.12 (main, Dec 17 2025, 21:10:06) [Clang 21.1.4 ] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sample_project
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ModuleNotFoundError: No module named 'sample_project'

The issue is that we need pyproject.toml to indicate that the package sample_project lives in src/.

Testing

The import works now