`sheet_t::reinitialization()` doesn't provide an ordering guarantee

[sean-parent]

If the following sheet (from default.pme) is reinitialized, the order of initialization is indeterminate (order is determined by iterating a closed_hash_map). Because the ordering of initializion determines priorities, the sheet may give different result. As a work-around you can ensure that only values used in the initial update are initialized. In this case the fix is to remoce the initializer on distance. Although that give you consistent results on reinitialization the priority state is still indeterminate so an edit may give a different result.

sheet distance_calculator
{
input:
    unit        : 1;

interface:
    distance  : 15 * unit; /* remove this initializer */
    rate        : 3 * unit;
    time        : 5 * unit;

logic:
    relate {
        rate <== distance / time;
        time <== distance / rate;
        distance <== rate * time;
    }
};