uv work: implement oldest dependencies into pyproject.toml

[clintonsteiner]

Fixes #806

[akaihola]

Why is uv sync --all-packages needed before running uv build?

Seems unrelated to testing with oldest dependencies?

[akaihola]

I ran uv build in this branch, and now the long description in PKG_INFO in the source distribution contains the HTML table for contributors. This is not desired since PyPI is not able to render raw HTML (see build #2766):

Checking dist/darker-2.1.1-py3-none-any.whl: FAILED
ERROR    `long_description` has syntax errors in markup and would not be        
         rendered on PyPI.                                                      
         line 974: Warning: "raw" directive disabled.                           
Checking dist/darker-2.1.1.tar.gz: FAILED
ERROR    `long_description` has syntax errors in markup and would not be        
         rendered on PyPI.                                                      
         line 974: Warning: "raw" directive disabled. 

When migrating from setup.cfg to pyproject.toml, we need ensure setup.py still gets run, reads README.rst, removes the contributor table, and uses the result as the long description.

The solution is to remove [tool.setuptools.dynamic] section and the readme = definition inside it. See this comment for details.

(This PR essentially fixes #806 which also explains the README issue.)