refactor: Use SpanReader over DataStream

This refactor does not change behavior. However, it avoids a vector
copy, which can lead to a minimal speed-up of 1%-5%, depending on the
call-site. This is mostly relevant for the fuzz tests and utils that
read large blobs of data (like a full block).

src/qt/test/wallettests.cpp

@@ -365,7 +365,7 @@ void TestGUI(interfaces::Node& node, const std::shared_ptr<CWallet>& wallet)
     std::vector<std::string> requests = walletModel.wallet().getAddressReceiveRequests();
     QCOMPARE(requests.size(), size_t{1});
     RecentRequestEntry entry;
-    DataStream{MakeUCharSpan(requests[0])} >> entry;
+    SpanReader{MakeByteSpan(requests[0])} >> entry;
     QCOMPARE(entry.nVersion, int{1});
     QCOMPARE(entry.id, int64_t{1});
     QVERIFY(entry.date.isValid());