Fix #372: Consider leaf-off litter and event fluxes in negative-growt…

[coder-Yash886]

Closes #372
Summary
This PR updates checkNegativeCreation() in src/sipnet/limitations.c to account for leaf-off litter (both computed phenology leaf-off and event leaf-off) and event biomass fluxes, as well as coarse root deductions for leaf-on allocations when performing the negative-growth look-ahead limitation check.

Previously, checkNegativeCreation() used continuous leaf turnover rate (envi.plantLeafC * params.leafTurnoverRate) and ignored phenology leaf-off litter, event leaf-off litter, event leaf/root fluxes, and leaf-on allocations. This could result in negative pool deficits not being properly detected and reallocated during timesteps with leaf-off or event fluxes.

Proposed Changes

1. Model Logic (src/sipnet/limitations.c)
   Leaf Deficit: Updated calculation to use fluxes.leafLitter (which includes both continuous turnover and computed phenology leaf-off litter), fluxes.eventLeafOffLitter, fluxes.leafOnCreation, fluxes.eventLeafC, and fluxes.eventLeafOnCreation.
   Fine Root Deficit: Updated calculation to include fluxes.eventFineRootC.
   Coarse Root Deficit: Updated calculation to include fluxes.eventCoarseRootC, as well as coarse root deductions for leaf-on allocations (leafOnFromRoot and eventLeafOnFromRoot).
   Carbon Balance: Verified that reallocations between sibling pools (leafCreation
   ↔
   ↔ woodCreation and fineRootCreation
   ↔
   ↔ coarseRootCreation) preserve exact total carbon creation across biomass pools.
2. Unit Tests (tests/sipnet/test_modeling/testFluxCalculations.c)
   Added testLeafOffAndEventDeficits() to test:
   Phenology leaf-off litter triggering leaf deficit reallocation to wood.
   Event leaf-off litter (eventLeafOffLitter) triggering leaf deficit reallocation to wood.
   Event root biomass fluxes and leaf-on root allocations in fine/coarse root deficit calculations.
   Explicit verification of carbon conservation across biomass creation fluxes.
3. Smoke Test Reference Outputs (tests/smoke/)
   Updated reference outputs for russell_1, russell_2, and russell_3 to reflect the corrected negative growth allocations during event/leaf-off timesteps.

[coder-Yash886]

@mdietze @Alomir @dlebauer Please Review the Pr When you have free time

[coder-Yash886]

@Alomir @dlebauer Please Review the PR when you have the free time