[FIX] decimal_precision: avoid refreshing float precisions at each cache invalidation

Changing the decimal precision of float fields is a rare
operation, while cache clearing occurs fairly frequently.
Signaling a full registry change when the decimal precision
is changed (instead of a mere cache change) is therefore
a better trade-off, and more semantically correct as well.
This way we avoid the decimal precision refresh for each
invalidation.

Registry invalidation implies cache invalidation.