fix(powermetrics): report 0 W when powermetrics returns no samples

[davidberenstein1957]

What

ApplePowermetrics.get_details() now guards against an empty match list before averaging: if powermetrics produced no CPU Power: / GPU Power: lines it logs a warning and reports 0.0 W instead of nan. The CPU and GPU branches were identical, so they are now one loop.

Why

np.mean([]) returns nan and only emits a RuntimeWarning, so the surrounding except Exception never fired and nothing was logged. The NaN flowed through AppleSiliconChip._get_power into the tracker accumulators, and since NaN is absorbing under addition, one bad sample made energy_consumed, emissions and emissions_rate NaN for the remainder of the run — written to emissions.csv and POSTed to the API as bare NaN.

This is reachable in the field whenever the powermetrics sudoers rule is missing (empty log), and on machines where the cpu_power sampler emits no GPU Power: lines, where it happened on every single call.

Reporting 0 W understates rather than invalidates, and the warning makes the condition visible.

Verification

Two new cases in tests/test_powermetrics.py (test_get_details_without_samples, test_get_details_without_gpu_samples) both fail on master and pass with this change. uv run pytest tests/test_powermetrics.py -q -> 18 passed. The existing test_get_details is unchanged, confirming the non-empty path still behaves identically.

Note: uv run task lint reports pre-existing violations across the repo and uv run task format reformats ~120 unrelated files, so neither was applied wholesale; black --check is clean on the two touched files.

Closes #1306

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.43%. Comparing base (065d0e6) to head (dd71abc).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1345      +/-   ##
==========================================
+ Coverage   91.39%   91.43%   +0.04%     
==========================================
  Files          49       49              
  Lines        5056     5058       +2     
==========================================
+ Hits         4621     4625       +4     
+ Misses        435      433       -2     

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