Add get_display_precision() to const.py returning DISPLAY_PRECISION_SUBUNIT (2)
or DISPLAY_PRECISION_BASE (4) based on config. Replace hardcoded round(..., 2)
with get_display_precision() in all calculators and attribute builders.
Add _update_suggested_precision() to sensor core; syncs entity registry
suggested_display_precision on every coordinator update.
Interval price sensors get full precision (2 or 4 dp); other MONETARY sensors
get half precision (1 or 2 dp) as sensible default.
Impact: Price sensor states and attributes now correctly use 4 decimal places
in base-currency mode (was always 2). Display precision in dashboards updates
automatically when currency mode changes.
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