Implement EIP-7823 and EIP-7825 for Osaka

EIP-7823: Reject ModExp inputs where any of baseLen/expLen/modLen
exceeds 1024 bytes (consume all gas, return OOG).

EIP-7825: Cap transaction gas limit at 2^24 (16,777,216) for Osaka+.

All 44,035 EEST tests passing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Giulio2002

host/evm.go

@@ -278,6 +278,11 @@ func (evm *Evm) Transact(tx *Transaction) ExecutionResult {
 		}
 	}
 
+	// EIP-7825 (Osaka): transaction gas limit cap
+	if evm.ForkID.IsEnabledIn(spec.Osaka) && tx.GasLimit > spec.TxGasLimitCap {
+		return haltResult(vm.InstructionResultFatalExternalError)
+	}
+
 	// Check tx gas limit <= block gas limit
 	blockGasLimit := evm.Block.GasLimit.AsUsize()
 	if tx.GasLimit > blockGasLimit {

precompiles/modexp.go

@@ -44,6 +44,11 @@ func modexpRun(input []byte, gasLimit uint64, model modexpModel) PrecompileResul
 	expLen := parseModexpLen(input[32:64])
 	modLen := parseModexpLen(input[64:96])
 
+	// EIP-7823 (Osaka): reject inputs where any length exceeds 1024 bytes.
+	if model == modexpOsaka && (baseLen > 1024 || expLen > 1024 || modLen > 1024) {
+		return PrecompileErr(PrecompileErrorOutOfGas)
+	}
+
 	// Gas calculation.
 	gasUsed := modexpGas(baseLen, expLen, modLen, input, model)
 	if gasUsed > gasLimit {