chore: improve python-devtools maintenance path

[lphuc2250gma]

Summary:

• Add a small unit test in tests/test_timer.py covering an under-exercised edge case of devtools.timer.Timer — e.g. calling .summary() before any .capture() lap (verify it does not divide by zero and produces a sensible string), and/or that nested context-manager usage of Timer records the expected number of laps. Pure additive test, no behavior change.
• Keep the change narrow so it is straightforward to review.

Notes:

• I kept this scoped to the relevant implementation and tests.