Revert "Make DEFAULT_EVENTS_PER_MAILBOX unreachable (#14843)" to stable 25-1 (#15509)

Author: naspirato

ydb/library/actors/core/config.h

@@ -13,7 +13,7 @@ namespace NActors {
 
     struct TBasicExecutorPoolConfig {
         static constexpr TDuration DEFAULT_TIME_PER_MAILBOX = TDuration::MilliSeconds(10);
-        static constexpr ui32 DEFAULT_EVENTS_PER_MAILBOX = 1'000'000;
+        static constexpr ui32 DEFAULT_EVENTS_PER_MAILBOX = 100;
 
         ui32 PoolId = 0;
         TString PoolName;