fix: double interest on pending redistribution

[danielattilasimon]

Addresses a bug that was found while reading the code.

The failing scenario was (implemented as test case testNoDoubleInterestOnPendingRedistribution):

1. A, B, C, D each open Troves having 10'000 BOLD debt, 100% interest rate p.a.
2. 1 year passes.
3. A, B, C get liquidated through redistribution.
4. D changes their interest rate to 10%.

The logs without the fix:

Logs:
  Trove D debt (initial)  : 10000.000000000000000000
  Trove D debt (post-1y)  : 20000.000000000000000000
  Trove D debt (post-liq) : 80000.000000000000000000
  Trove D debt (post-adj) : 140000.000000000000000000

Everything looks good up until immediately post-liquidation. Each Trove's debt doubles as expected, 3 of them get redistributed to D, thus D's debt is 80'000 BOLD.

But then, when D adjusts their interest rate, their debt immediately increases by a whopping 60K! This is an invariant violation; a Trove's debt should not be changed by adjusting the interest rate, unless time also passes inbetween.

The root cause is that we apply the redistribution first — which involves calculating the interest on the debt that's being redistributed — and then perform interest rate calculation on the new debt — which includes debt to which interest has already been added.

[danielattilasimon]

This is the actual fix. Every other change is just auto-formatting.

[bingen]

LGTM! Good find, thanks!

[RickGriff]

Looks good!