ledger-tool cap: output credits_observed (#13746) (#13747)

(cherry picked from commit 3bc7d85986)

Co-authored-by: Ryo Onodera <ryoqun@gmail.com>

programs/stake/src/stake_state.rs

@@ -37,6 +37,7 @@ pub enum InflationPointCalculationEvent {
     RentExemptReserve(u64),
     Delegation(Delegation, Pubkey),
     Commission(u8),
+    CreditsObserved(u64),
 }
 
 fn null_tracer() -> Option<impl FnMut(&InflationPointCalculationEvent)> {
@@ -479,6 +480,11 @@ impl Stake {
         )
         .map(|(stakers_reward, voters_reward, credits_observed)| {
             self.credits_observed = credits_observed;
+            if let Some(inflation_point_calc_tracer) = inflation_point_calc_tracer {
+                inflation_point_calc_tracer(&InflationPointCalculationEvent::CreditsObserved(
+                    credits_observed,
+                ));
+            }
             self.delegation.stake += stakers_reward;
             (stakers_reward, voters_reward)
         })