Merge bitcoin/bitcoin#30094: rpc: move UniValue in blockToJSON

b77bad3 rpc: move UniValue in blockToJSON (willcl-ark)

Pull request description:

  Fixes: #24542
  Fixes: #30052

  Without explicitly declaring the move, these `UniValues` get copied, causing increased memory usage. Fix this by explicitly moving the `UniValue` objects.

  Used by `rest_block` and `getblock` RPC.

ACKs for top commit:
  maflcko:
    review ACK b77bad3
  ismaelsadeeq:
    ACK b77bad3
  TheCharlatan:
    ACK b77bad3
  theuni:
    utACK b77bad3
  hebasto:
    ACK b77bad3, I have reviewed the code and it looks OK.
  BrandonOdiwuor:
    ACK b77bad3

Tree-SHA512: 767608331040f9cfe5c3568ed0e3c338920633472a1a50d4bbb47d1dc69d2bb11466d611f050ac8ad1a894b47fe1ea4d968cf34cbd44d4bb8d479fc5c7475f6d

Author: ryanofsky

src/rpc/blockchain.cpp

@@ -279,12 +279,12 @@ UniValue blockToJSON(const CBlock& block, const CBlockIndex* tip, const CBlockIn
                 const CTxUndo* txundo = (have_undo && i > 0) ? &blockUndo.vtxundo.at(i - 1) : nullptr;
                 UniValue objTx(UniValue::VOBJ);
                 TxToUniv(*tx, uint256(), objTx, true, RPCSerializationFlags(), txundo, verbosity);
-                txs.push_back(objTx);
+                txs.push_back(std::move(objTx));
             }
             break;
     }
 
-    result.pushKV("tx", txs);
+    result.pushKV("tx", std::move(txs));
 
     return result;
 }