Merge #20464: refactor: Treat CDataStream bytes as uint8_t

fa29272459 Remove redundant MakeUCharSpan wrappers (MarcoFalke)
faf4aa2f47 Remove CDataStream::Init in favor of C++11 member initialization (MarcoFalke)
fada14b948 Treat CDataStream bytes as uint8_t (MarcoFalke)
fa8bdb048e refactor: Drop CDataStream constructors in favor of one taking a Span of bytes (MarcoFalke)
faa96f841f Remove unused CDataStream methods (MarcoFalke)

Pull request description:

  Using `uint8_t` for raw bytes has a style benefit:
  * The signedness is clear from reading the code, as it does not depend on the architecture

  Other clean-ups in this pull include:
  * Remove unused methods
  * Constructor is simplified with `Span`
  * Remove `Init()` member in favor of C++11 member initialization

ACKs for top commit:
  laanwj:
    code review ACK fa29272459
  theStack:
    ACK fa29272459 🍾

Tree-SHA512: 931ee28bd99843d7e894b48e90e1187ffb0278677c267044b3c0c255069d9bbd9298ab2e539b1002a30b543d240450eaec718ef4ee95a7fd4be0a295e926343f

src/qt/walletmodel.cpp

@@ -245,7 +245,7 @@ WalletModel::SendCoinsReturn WalletModel::sendCoins(WalletModelTransaction &tran
 
         CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
         ssTx << *newTx;
-        transaction_array.append(&(ssTx[0]), ssTx.size());
+        transaction_array.append((const char*)&(ssTx[0]), ssTx.size());
     }
 
     // Add addresses / update labels that we've sent to the address book,