chore: make CallOnFlush/CallOnEvict/CallOnDiskRead default to false via DIM

All three gate properties on IRecordTriggers now have default implementations
returning false. Implementations that don't need any trigger callbacks (like
GarnetRecordTriggers) no longer need to explicitly declare them — the empty
struct body suffices.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: badrishc

libs/server/Storage/Functions/GarnetRecordTriggers.cs

@@ -13,13 +13,5 @@ namespace Garnet.server
     /// </summary>
     public readonly struct GarnetRecordTriggers : IRecordTriggers
     {
-        /// <inheritdoc/>
-        public bool CallOnFlush => false;
-
-        /// <inheritdoc/>
-        public bool CallOnEvict => false;
-
-        /// <inheritdoc/>
-        public bool CallOnDiskRead => false;
     }
 }

libs/server/Storage/Functions/MainStore/RMWMethods.cs

@@ -1706,7 +1706,6 @@ public readonly bool PostCopyUpdater<TSourceLogRecord>(in TSourceLogRecord srcLo
             if (functionsState.appendOnlyFile != null)
                 rmwInfo.UserData |= NeedAofLog; // Mark that we need to write to AOF
 
-            // Account for the new record's value-side heap contribution.
             return true;
         }
 

libs/storage/Tsavorite/cs/src/core/Allocator/AllocatorBase.cs

@@ -1426,9 +1426,8 @@ internal void EvictPageForRecovery(long page)
             {
                 _wrapper.EvictRecordsInRange(start, end, source);
             }
-            else if (onEvictionObserver is not null)
+            if (onEvictionObserver is not null)
             {
-                // Legacy observer path for consumers still using SubscribeEvictions.
                 MemoryPageScan(start, end, onEvictionObserver);
             }
 

libs/storage/Tsavorite/cs/src/core/Index/StoreFunctions/IRecordTriggers.cs

@@ -31,21 +31,21 @@ public interface IRecordTriggers
         /// If true, <see cref="OnFlush(ref LogRecord)"/> is called per valid record on the
         /// original in-memory page before it is flushed to disk.
         /// </summary>
-        bool CallOnFlush { get; }
+        bool CallOnFlush => false;
 
         /// <summary>
         /// If true, <see cref="OnEvict(ref LogRecord, EvictionSource)"/> is called per non-tombstoned
         /// record when a page is evicted past HeadAddress. Returning false lets the allocator skip the
         /// per-record OnEvict callback when the application has no work to do.
         /// Note: Tsavorite's internal heap-size accounting runs regardless of this flag.
         /// </summary>
-        bool CallOnEvict { get; }
+        bool CallOnEvict => false;
 
         /// <summary>
         /// If true, <see cref="OnDiskRead(ref LogRecord)"/> is called per record loaded from
         /// disk into memory (recovery, delta log apply, pending reads, push scans).
         /// </summary>
-        bool CallOnDiskRead { get; }
+        bool CallOnDiskRead => false;
 
         /// <summary>
         /// Called when a record is disposed due to delete, expiration, CAS failure, elision,