Implementing .flake8 and PEP8 linting

[gnzng]

I would like to work on Flake8 integration for the project. Flake8 is a popular linting tool that helps maintain code quality by enforcing style guidelines and identifying potential errors in Python code. It is added on the IDE side and configured through a synched .flake8 file.

The roadmap to make these changes I would suggest the following:

PR #36 will pinpoint the current codebase to version 0.3.0. We can then start implementing the following changes:

1. test files + adding .flake8
2. aux files
3. implementing changes to files which are not touched by the active / WIP forks

• [feature] Multi-GPU support #17
• [WIP] Add support for holography reconstructions and single frame CDI-like reconstructions #27
• [WIP] Adding near field ptychography #31

3. letting the WIP forks implement the flake8 changes over time or after merged into master
4. include flake8 in CI / workflow