X1 Hybrid Gen4: fix battery current sign, add Load power and Run Mode

[bjorn-ioronksen]

What

For the X1HybridGen4 inverter (API type: 15):

1. Fix battery current sign. Register 15 is signed, but it was decoded with div100 alone. On a discharging battery that produces a large positive number (I saw ~652 A). twoway_div100 gives the correct signed value.
2. Add Load power (register 38, to_signed).
3. Add Inverter Run Mode (register 10, raw enum, same table as X3HybridG4).

Why

My inverter (type: 15, ver: 3.019.01) reports battery current as 65316 while discharging ~250 W at ~115 V. div100 → 653.16 A. twoway_div100 → to_signed(65316)/100 → -2.2 A, which matches battery power / battery voltage (-252 W / 114.9 V).

The two extra registers are useful and already validated by the fixtures.

Tests

• Adds X1_HYBRID_GEN4_V_3_019_RESPONSE / _VALUES: a real ReadRealTimeData capture from a discharging type: 15 inverter (the case the sign bug affected). Serial fields sanitised.
• Updates the two existing X1HybridGen4 expected-value dicts (X1_HYBRID_G4_VALUES, X1_HYBRID_G4_V_3_018_VALUES) with Load power and Inverter Run Mode. Battery current is unchanged for both (their raw values are small positives, so twoway_div100 == div100 there).
• pytest: 191 passed, 135 skipped. flake8 clean.

Note

Inverter Run Mode reads 2 ("Normal") across all three fixtures; a maintainer with another type: 15 unit confirming register 10 would be welcome. A decoded text variant (like X3HybridG4's "Run mode text") could be added later.

[bjorn-ioronksen]

Heads up on CI: the black --check step also flags solax/inverter.py and solax/response_parser.py, which this PR doesn't touch. That's pre-existing: the workflow does pip install --upgrade black (unpinned), so it now pulls black 26.x whose 2026 stable style reformats those two files. It fails the same way on a clean master. My additions are formatted with current black. Happy to either pin black in the workflow or run black . as a separate commit here, whichever you prefer.

[bjorn-ioronksen]

Updated: reverted the black-reformat commit, this PR is now just the X1 Hybrid Gen4 change.

The CI failures on this branch are pre-existing, not from this PR. The workflow does pip install --upgrade for both black and pylint (unpinned), and the current versions flag existing code:

• black --check wants to reformat solax/inverter.py and solax/response_parser.py (fails the same on a clean master)
• pylint flags solax/response_parser.py:49 C0103 on GenericResponseSchema

My additions pass black, isort, flake8, mypy and pylint locally. Pinning the linters in the workflow would make CI meaningful again; happy to do that as a separate PR if useful.