[ENH] Add test to validate execution of README Python examples

[PredictiveManish]

Adds a pytest that parses README.md and executes all python code blocks to ensure examples remain valid.

Closes #669

• Uses regex to extract Python blocks
• Executes them sequentially in a shared namespace (since examples are stateful)
• Runs from repo root so relative paths like tests/resources/... resolve correctly
• Adds repo root to sys.path so pypfopt can be imported without installation

This verifies that README examples run as documented and helps prevent regressions in imports or usage.

[PredictiveManish]

The extra file changes occurred when I started working on the CI failure issue, as Ruff auto-formatting modified some files.

and as it's not any logic break or any particular change so I added them here.