Merge bitcoin/bitcoin#32176: net: Prevent accidental circuit sharing when using Tor stream isolation

ec81a72b36 net: Add randomized prefix to Tor stream isolation credentials (laanwj)
c47f81e8ac net: Rename `_randomize_credentials` Proxy parameter to `tor_stream_isolation` (laanwj)

Pull request description:

  Add a class TorsStreamIsolationCredentialsGenerator that generates unique credentials based on a randomly generated session prefix and an atomic counter. Use this in `ConnectThroughProxy` instead of a simple atomic int counter.

  This makes sure that different launches of the application won't share the same credentials, and thus circuits, even in edge cases.

  Example with `-debug=proxy`:
  ```
  2025-03-31T16:30:27Z [proxy] SOCKS5 sending proxy authentication 0afb2da441f5c105-0:0afb2da441f5c105-0
  2025-03-31T16:30:31Z [proxy] SOCKS5 sending proxy authentication 0afb2da441f5c105-1:0afb2da441f5c105-1
  ```

  Thanks to hodlinator in https://github.com/bitcoin/bitcoin/pull/32166#discussion_r2020973352 for the idea.

ACKs for top commit:
  hodlinator:
    re-ACK ec81a72b36
  jonatack:
    ACK ec81a72b36
  danielabrozzoni:
    tACK ec81a72b36

Tree-SHA512: 195f5885fade77545977b91bdc41394234ae575679cb61631341df443fd8482cd74650104e323c7dbfff7826b10ad61692cca1284d6810f84500a3488f46597a

src/qt/optionsdialog.cpp

@@ -482,7 +482,7 @@ QValidator::State ProxyAddressValidator::validate(QString &input, int &pos) cons
     if (!SplitHostPort(input.toStdString(), port, hostname) || port != 0) return QValidator::Invalid;
 
     CService serv(LookupNumeric(input.toStdString(), DEFAULT_GUI_PROXY_PORT));
-    Proxy addrProxy = Proxy(serv, true);
+    Proxy addrProxy = Proxy(serv, /*tor_stream_isolation=*/true);
     if (addrProxy.IsValid())
         return QValidator::Acceptable;