feat(tracing): enable external tracer registration and VM inheritance

src/Nethermind/Nethermind.Blockchain/Tracing/GethStyle/Custom/Native/GethLikeNativeTracerFactory.cs

@@ -31,7 +31,7 @@ private static void RegisterNativeTracers()
         RegisterTracer(NativeCallTracer.CallTracer, static (options, _, transaction, _) => new NativeCallTracer(transaction, options));
     }
 
-    private static void RegisterTracer(string tracerName, GethLikeNativeTracerFactoryDelegate tracerDelegate)
+    public static void RegisterTracer(string tracerName, GethLikeNativeTracerFactoryDelegate tracerDelegate)
     {
         _tracers.Add(tracerName, tracerDelegate);
     }

src/Nethermind/Nethermind.Evm/GasPolicy/EthereumGasPolicy.cs

@@ -169,6 +169,12 @@ public static bool ConsumeLogEmission(ref EthereumGasPolicy gas, long topicCount
     public static void ConsumeDataCopyGas(ref EthereumGasPolicy gas, bool isExternalCode, long baseCost, long dataCost)
         => Consume(ref gas, baseCost + dataCost);
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static void OnBeforeInstructionTrace(in EthereumGasPolicy gas, int pc, Instruction instruction, int depth) { }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static void OnAfterInstructionTrace(in EthereumGasPolicy gas) { }
+
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static EthereumGasPolicy Max(in EthereumGasPolicy a, in EthereumGasPolicy b) =>
         a.Value >= b.Value ? a : b;

src/Nethermind/Nethermind.Evm/GasPolicy/IGasPolicy.cs

@@ -215,4 +215,21 @@ static abstract bool UpdateMemoryCost(ref TSelf gas,
     /// <param name="baseCost">Fixed opcode cost.</param>
     /// <param name="dataCost">Per-word copy cost.</param>
     static abstract void ConsumeDataCopyGas(ref TSelf gas, bool isExternalCode, long baseCost, long dataCost);
+
+    /// <summary>
+    /// Hook called before instruction execution when tracing is active.
+    /// Allows gas policies to capture pre-execution state.
+    /// </summary>
+    /// <param name="gas">The current gas state.</param>
+    /// <param name="pc">The program counter before incrementing.</param>
+    /// <param name="instruction">The instruction about to be executed.</param>
+    /// <param name="depth">The current call depth.</param>
+    static abstract void OnBeforeInstructionTrace(in TSelf gas, int pc, Instruction instruction, int depth);
+
+    /// <summary>
+    /// Hook called after instruction execution when tracing is active.
+    /// Allows gas policies to capture post-execution state.
+    /// </summary>
+    /// <param name="gas">The current gas state after execution.</param>
+    static abstract void OnAfterInstructionTrace(in TSelf gas);
 }

src/Nethermind/Nethermind.Evm/VirtualMachine.cs

@@ -1250,6 +1250,9 @@ protected virtual unsafe CallResult RunByteCode<TTracingInst, TCancelable>(
                 if (TCancelable.IsActive && _txTracer.IsCancelled)
                     ThrowOperationCanceledException();
 
+                // Call gas policy hook before instruction execution.
+                TGasPolicy.OnBeforeInstructionTrace(in gas, programCounter, instruction, VmState.Env.CallDepth);
+
                 // If tracing is enabled, start an instruction trace.
                 if (TTracingInst.IsActive)
                     StartInstructionTrace(instruction, TGasPolicy.GetRemainingGas(in gas), programCounter, in stack);
@@ -1278,6 +1281,10 @@ protected virtual unsafe CallResult RunByteCode<TTracingInst, TCancelable>(
                     OpCodeCount += opCodeCount;
                     goto OutOfGas;
                 }
+
+                // Call gas policy hook after instruction execution.
+                TGasPolicy.OnAfterInstructionTrace(in gas);
+
                 // If an exception occurred, exit the loop.
                 if (exceptionType != EvmExceptionType.None)
                     break;