Qt backend does not compile against an SSL-less Qt (QT_NO_SSL / wasm)

[Yaraslaut]

Summary

QtWebSocketBackend unconditionally includes <QSslConfiguration>, takes a
std::optional<QSslConfiguration> constructor parameter, and stores one as a member.

Qt builds configured without SSL define QT_NO_SSL and do not provide that type. The Qt for
WebAssembly build is the common case — TLS is terminated by the browser, so Qt ships no SSL
backend. Against such a Qt the header does not compile.

Reproduction

Build any translation unit including morph/qt/qt_websocket_backend.hpp against a Qt
configured with -no-ssl (or the standard wasm Qt):

fatal error: 'QSslConfiguration' file not found

Why it matters

It's a hard compile failure rather than a degraded feature: the whole Qt backend becomes
unavailable on a target where the WebSocket transport itself works fine. wss:// still works
on that target too — the page's TLS is handled by the browser before Qt sees the socket — so
the only thing genuinely absent is the ability to configure TLS from C++.

Suggested fix

Guard the SSL surface, leaving everything else intact:

#ifndef QT_NO_SSL
#  include <QSslConfiguration>
#endif

    explicit QtWebSocketBackend(
        QUrl serverUrl,
        /* ... */
#ifndef QT_NO_SSL
        std::optional<QSslConfiguration> tls = std::nullopt,
#endif
        Config cfg = Config{});

private:
#ifndef QT_NO_SSL
    std::optional<QSslConfiguration> _tls;
#endif

plus the corresponding guards around the .cpp uses.

A note in the class docs that the parameter is absent on SSL-less builds — and why wss://
nonetheless works there — would save the next person the same investigation.

Trade-off worth naming: this makes the constructor signature vary by build configuration.
The alternative — keeping the parameter and ignoring it — isn't available, since the type
doesn't exist. If you'd rather express it as a distinct tlsConfig() setter that simply isn't
declared under QT_NO_SSL, that keeps the constructor stable and I'm happy to do it that way.

Happy to open a PR.