Smoother migration toward new preservation cycles

For now, the set of the preservation cycles constant to 1 is handled automatically by the store. Thus, the store will create a big cemented chunk containing 5 cycles as soon as the new constant kicks in.

├── 0_1
├── 10_17
├── 18_25
├── 26_33
├── 2_9
├── 34_73 <---
├── 74_81
├── 82_89
├── 90_97
├── 98_105

To avoid this a conform the usual cemented store's shape, that is split into cycles, we may want to perform a smoother transition thanks to a protocol plug-in.