clients/go-ethereum, clients/nethermind: pin gas-limit target via HIVE_TARGET_GAS_LIMIT

Without an explicit target, geth and Nethermind use different default
gas-limit policies under the engine API: geth's CalcGasLimit moves the
parent gas limit toward miner.gaslimit (default 60M) by 1/1024 per
block, while Nethermind keeps the parent gas limit unchanged unless
Blocks.TargetBlockGasLimit is set. With the rpc-compat chain head sitting
at ~75M, the two clients diverge from block 1 onward, so blocks produced
by testing_buildBlockV1 / testing_commitBlockV1 in rpc-compat replay get
different hashes between clients and the strict-match tests fail on
Nethermind.

Wiring a new HIVE_TARGET_GAS_LIMIT env var through geth.sh
(--miner.gaslimit) and Nethermind's mkconfig.jq (Blocks.TargetBlockGasLimit)
makes both clients target the same ceiling. With the value set to
60000000 in execution-apis/tools/chain/forkenv.json, CalcGasLimit
produces the same gas limit at every step on both clients, so the
recorded rpc-compat fixtures replay byte-exact on both.

Spec and cross-client fixtures: ethereum/execution-apis#801

Author: MysticRyuujin

clients/go-ethereum/geth.sh

@@ -136,6 +136,9 @@ fi
 if [ "$HIVE_MINER_EXTRA" != "" ]; then
     FLAGS="$FLAGS --miner.extradata $HIVE_MINER_EXTRA"
 fi
+if [ "$HIVE_TARGET_GAS_LIMIT" != "" ]; then
+    FLAGS="$FLAGS --miner.gaslimit $HIVE_TARGET_GAS_LIMIT"
+fi
 
 # Configure RPC.
 FLAGS="$FLAGS --http --http.addr=0.0.0.0 --http.port=8545 --http.api=admin,debug,eth,miner,net,txpool,web3,testing"

clients/nethermind/mkconfig.jq

@@ -46,14 +46,14 @@ def json_rpc_config:
     {
       "JsonRpc": {
         "JwtSecretFile": "/jwt.secret",
-        "EnabledModules": ["Debug", "Eth", "Subscribe", "Trace", "TxPool", "Web3", "Personal", "Proof", "Net", "Parity", "Health", "Admin"],
+        "EnabledModules": ["Debug", "Eth", "Subscribe", "Trace", "TxPool", "Web3", "Personal", "Proof", "Net", "Parity", "Health", "Admin", "Testing"],
         "AdditionalRpcUrls": ["http://0.0.0.0:8550|http;ws|debug;net;eth;subscribe;engine;web3;client;admin|no-auth", "http://0.0.0.0:8551|http;ws|debug;net;eth;subscribe;engine;web3;client;admin"]
       }
     }
   else
     {
       "JsonRpc": {
-        "EnabledModules": ["Debug", "Eth", "Subscribe", "Trace", "TxPool", "Web3", "Personal", "Proof", "Net", "Parity", "Health", "Admin"]
+        "EnabledModules": ["Debug", "Eth", "Subscribe", "Trace", "TxPool", "Web3", "Personal", "Proof", "Net", "Parity", "Health", "Admin", "Testing"]
       }
     }
   end
@@ -79,6 +79,18 @@ def txpool_config:
   end
 ;
 
+def blocks_config:
+  if env.HIVE_TARGET_GAS_LIMIT != null then
+    {
+      "Blocks": {
+        "TargetBlockGasLimit": (env.HIVE_TARGET_GAS_LIMIT | tonumber)
+      }
+    }
+  else
+    {}
+  end
+;
+
 def base_config:
   {
     "Init": {
@@ -116,4 +128,4 @@ def base_config:
 ;
 
 # This is the main expression that outputs the config.
-base_config * keystore_config * merge_config * json_rpc_config * sync_config * txpool_config
+base_config * keystore_config * merge_config * json_rpc_config * sync_config * txpool_config * blocks_config