Changes

ruff.toml: new file

Add a file in the root dir of the repository to allow running
"ruff format" in order to auto-format the code with expected max line
length, PEP-8, etc.

Replace _testenv/pyproject.toml with .ruff.toml in the root directory of
the repository, so we can exclude "compare-results.py" which doesn't
follow that code style. Otherwise it would get formatted too when
running "ruff format" in the root dir of the repository.

Change-Id: I97ed1ececba85008ca754cf91bf46522e168a894