Fix non-string unit_of_measurement 500-ing /api/states on HA 2026.7+

[Austin519]

Problem

On Home Assistant 2026.7+, adding this integration returns HTTP 500 for the entire /api/states endpoint (the whole dashboard/app becomes unusable), not just a single broken entity.

Root cause: several register definitions in const.py pass a TextReadEntityType instance as the positional unit argument of RegisterInfo(...) (numeric registers reusing an enum for display). Those entities then get a non-string unit_of_measurement — the TextReadEntityType object itself. HA 2026.7 tightened its state serializer, which now raises:

TypeError: Type is not JSON serializable: TextReadEntityType

Because that happens in the shared /api/states serialization path, it fails the whole response, taking every entity down with it. Example offender: vebus Microgrid error (state_class=measurement, unit_of_measurement=<TextReadEntityType object>).

Fix

Coerce any non-string unit to None when building the entity description, in both sensor.py and number.py:

native_unit_of_measurement=(registerInfo.unit if isinstance(registerInfo.unit, str) else None),

Minimal and safe — text/enum entities have no meaningful unit anyway, and their value decoding (in sensor.py) is unchanged. This guards at the description layer regardless of which const.py entries carry the bad unit.

Testing

• HA 2026.7.4, Cerbo GX (3-phase ESS + FischerPanda genset), advanced mode, 657 entities.
• Before: /api/states → 500; log shows the TextReadEntityType TypeError above.
• After: /api/states → 200; all entities (incl. the writable number/select/switch/button controls) load and operate normally.