replaced raw void* with std::any

[orange-cpp]

Updates the way user data is managed in the crow::websocket::connection class, replacing the use of raw pointers with a safer and more flexible and memory safe approach.

Improvements to user data handling:

• Changed the userdata_ member from a void* to a std::any, allowing storage of arbitrary types and improving type safety.
• Updated the userdata() setter and getter methods to use std::any instead of void*, enabling safer and more flexible user data management.

Why it's important:

CROW_WEBSOCKET_ROUTE(app, "/ws")
      .onopen([&](crow::websocket::connection& conn) {
          conn.userdata(std::make_shared<Foo>());
          CROW_LOG_INFO << "new websocket connection from " << conn.get_remote_ip();
          std::lock_guard<std::mutex> _(mtx);
          users.insert(&conn);
      })
      .onclose([&](crow::websocket::connection& conn, const std::string& reason, uint16_t) {
          CROW_LOG_INFO << "websocket connection closed: " << reason;
          std::lock_guard<std::mutex> _(mtx);
          users.erase(&conn);
      })
      .onmessage([&](crow::websocket::connection& /*conn*/, const std::string& data, bool is_binary) {
          std::lock_guard<std::mutex> _(mtx);
          for (auto u : users)
              if (is_binary)
                  u->send_binary(data);
              else
                  u->send_text(data);
      });

Output:

(2026-02-21 06:23:37) [INFO    ] Crow/master server is running at http://0.0.0.0:40080 using 28 threads
(2026-02-21 06:23:37) [INFO    ] Call `app.loglevel(crow::LogLevel::Warning)` to hide Info level logs.
Foo(): Allocated user data
(2026-02-21 06:23:38) [INFO    ] new websocket connection from 127.0.0.1
~Foo(): Deallocated user data
(2026-02-21 06:23:41) [INFO    ] websocket connection closed: 

You see client code can have huge .onclose handler and you can forgot call delete on object wich leads to memory leak or you can miss-cast type into something else and get UB wich is even worse.

[orange-cpp]

Fixed missing #include <any> that fail fuzzing pipeline waiting for approval.

[gittiver]

any has value characteristics, so there should be at least test to check if it behaves correctly?

[orange-cpp]

any has value characteristics, so there should be at least test to check if it behaves correctly?

Tested it in my pet projects works very nicely, with smart pointers and any other types. Should be good to merge

[gittiver]

set back to drift as no documentation and no tests were provided.