Split charge windows at dawn for any combine_charge_slots user, not just low power mode

[springfall2008]

Summary

• calc_dawn() (added for Low power charge toggle does nothing #4557) splits a charge window at the light/dark PV boundary so a window spanning sunrise doesn't get treated as one indivisible block. It was only ever computed when set_charge_low_power was on.
• But the split only matters when combine_charge_slots is on in the first place — with it off, find_charge_window already forces a break every charge_slot_split minutes (= plan_interval_minutes, the same granularity calc_dawn buckets at), so the dawn boundary can never be reached and computing it was a no-op there.
• That gating also meant combine_charge_slots users without low power charging never got the split, even though it has a benefit independent of low power: it lets the plan optimizer charge just the dark portion of a combined window and skip the daylight portion where solar may cover the load.
• New calc_pv_light_dark() decides whether to call calc_dawn(), gated on combine_charge_slots instead of set_charge_low_power.
• calc_dawn() now also logs the calculated dawn time each cycle it runs, so it's visible in the log whether the detected dawn looks sane.

Test plan

• ./run_all --test find_charge_window — new test_calc_pv_light_dark covers all four combine_charge_slots × set_charge_low_power combinations; existing test_calc_dawn and Path J (pv_light_dark boundary) tests unaffected
• ./run_all --quick — full quick suite passes, including the random scenario plan regression against the committed baseline
• ./run_pre_commit — black/ruff/cspell/docstring coverage all pass

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR adjusts how Predbat splits charge windows at the PV light/dark (dawn) boundary so the split is applied for any user with combine_charge_slots enabled, rather than only when set_charge_low_power is enabled. This improves the planner’s ability to treat cheap-rate windows spanning sunrise as separable dark/light portions for optimization.

Changes:

• Add calc_pv_light_dark() to gate dawn-splitting on combine_charge_slots and update fetch_sensor_data() to use it.
• Enhance calc_dawn() documentation and add logging of the detected dawn time (or absence of one).
• Add a new unit test test_calc_pv_light_dark covering all combine_charge_slots × set_charge_low_power combinations.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
apps/predbat/fetch.py	Introduces calc_pv_light_dark() and switches dawn boundary computation to be driven by combine_charge_slots; adds dawn-time logging in calc_dawn().
apps/predbat/tests/test_find_charge_window.py	Adds test_calc_pv_light_dark and wires it into the existing test_find_charge_window test flow.

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