There is already a Python test. Add a few C tests as well, for bootstage
itself and for the 'bootstage' command.
Add helpers to access the internal state. Be careful to zero records
when removing them, since if the record is later reused, bootstage
expects the time to be zero.
Co-developed-by: Claude <noreply@anthropic.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
