ci: Add format check workflow

[pdgendt]

Add a CI workflow to report formatting issues on changed files. This is to gradually update files in the repository to be conform with PEP8 formatting.

[marc-hb]

Can this check be easily overriden ignored when needed? For instance we don't want one-line fix PRs to be drowned in whitespace changes.

[pdgendt]

Went a step further, new files are always fully checked, changed chunks now also need to be formatted.

Experimenting shown here: https://github.com/pdgendt/west/actions/workflows/format.yml with annotations

[marc-hb]

Checking only modified chunks sounds great in theory but I'm concerned that the code of the Github workflow is getting too complicated and hard to maintain. It's not like west has had an oversupply of maintainers :-/

As long as this check does not block merges, I think checking only new and modified files (the entire file each time) is a good enough trade-off. For sure that trade-off has been working well for years with pylint and shellcheck in thesofproject/sof-test@336094b

[pdgendt]

Checking only modified chunks sounds great in theory but I'm concerned that the code of the Github workflow is getting too complicated and hard to maintain. It's not like west has had an oversupply of maintainers :-/

As long as this check does not block merges, I think checking only new and modified files (the entire file each time) is a good enough trade-off. For sure that trade-off has been working well for years with pylint and shellcheck in thesofproject/sof-test@336094b

Updated the PR accordingly:

• Ignore deleted python files
• Run ruff format --check --diff on entire files
• Add continue-on-error: true to make the workflow pass if the format job fails (making it non-blocking)
• Add a warning annotation instead of an error

Most concerns addressed