Quality-only cleanups on the air-conditioner support, no behavior change:
- climate.py: reuse common.normalize_temp_unit for the C/F unit read (also
handles the "Celsius"/"Fahrenheit" long forms); collapse the three
fan/swing/preset read properties into _read_mode/_read_modes and the three
write setters into _set_mapped, removing the copy-paste.
- Single source of truth for the climate-consumed hrefs: they lived both as
constants in climate.py and as a list in airconditioner.py. Declare them
once in airconditioner.py (HREF_* + CLIMATE_CONSUMED_HREFS, which also builds
the COVERAGE caps) and import them into climate.py, so a new sibling read
can't drift out of sync with its coverage entry.