Implement repetition of files using pytest_collect_file hook: run
file collection as many times as needed to cover all --mode/--repeat
combinations. Also move disabled test logic to this hook.
Store build mode and run_id in pytest item stashes.
Simplify support of C++ tests: remove redundant facade abstraction and put
all code into 3 files: base.py, boost.py, and unit.py
Add support for `run_first` option in test_config.yaml
