jsonrpc: Add totalDifficulty back as interim hive fix (#12469)

Until hive implements
ethereum/execution-apis#570

Partial revert of https://github.com/erigontech/erigon/pull/11809/files

The reason this would still work with or without the snapshot files
change:
- RPC tests don't have to know about this PR, since it's based on a
state with assumed nil for the `totalDifficulty` field.
- Hive tests don't progress till pruning, nor do they start with any
snapshots (unless this changes somehow)

turbo/jsonrpc/eth_block.go

@@ -229,6 +229,16 @@ func (api *APIImpl) GetBlockByNumber(ctx context.Context, number rpc.BlockNumber
 	}
 	additionalFields := make(map[string]interface{})
 
+	// =============================
+	// TODO - remove this after https://github.com/ethereum/execution-apis/pull/570 is implemented by Hive and rest of the community
+	td, err := rawdb.ReadTd(tx, b.Hash(), b.NumberU64())
+	if err != nil {
+		return nil, err
+	}
+	if td != nil {
+		additionalFields["totalDifficulty"] = (*hexutil.Big)(td)
+	}
+	// =================================
 	chainConfig, err := api.chainConfig(ctx, tx)
 	if err != nil {
 		return nil, err
@@ -282,6 +292,17 @@ func (api *APIImpl) GetBlockByHash(ctx context.Context, numberOrHash rpc.BlockNu
 	}
 	number := block.NumberU64()
 
+	// =============================
+	// TODO - remove this after https://github.com/ethereum/execution-apis/pull/570 is implemented by Hive and rest of the community
+	td, err := rawdb.ReadTd(tx, hash, number)
+	if err != nil {
+		return nil, err
+	}
+	if td != nil {
+		additionalFields["totalDifficulty"] = (*hexutil.Big)(td)
+	}
+	// ==============================
+
 	chainConfig, err := api.chainConfig(ctx, tx)
 	if err != nil {
 		return nil, err