Incorrect category for OpenSSL errors

[anarthal]

openssl_stream seems to convert OpenSSL errors obtained from ERR_get_error by always assigning them std::system_category():

corosio/src/openssl/src/openssl_stream.cpp

Lines 602 to 605 in 5b59fe9

	unsigned long ssl_err = ERR_get_error();
	ec = std::error_code(
	static_cast<int>(ssl_err), std::system_category());
	co_return {ec};

This is not correct, as most OpenSSL errors are not system errors. The consequence is that OpenSSL generated errors display an incorrect message when using error_code::message() (or printing them).

For example, the following program triggers a TLS certificate validation error:

capy::task<void> run(corosio::io_context& ioc, corosio::ipv4_address addr, std::uint16_t port)
{
    // Create and connect a TCP socket
    corosio::tcp_socket sock(ioc);
    sock.open();
    if (auto [ec] = co_await sock.connect(corosio::endpoint(addr, port)); ec)
        throw std::system_error(ec, "TCP connect");

    // Configure TLS: verify the peer's certificate using the system CA store
    corosio::tls_context ctx;
    if (auto ec = ctx.set_default_verify_paths(); ec)
        throw std::system_error(ec, "set_default_verify_paths");
    if (auto ec = ctx.set_verify_mode(corosio::tls_verify_mode::peer); ec)
        throw std::system_error(ec, "set_verify_mode");
    ctx.set_hostname("www.boost.org");

    // Wrap the socket in a TLS stream and perform the handshake
    corosio::openssl_stream tls(&sock, ctx);
    auto [ec] = co_await tls.handshake(corosio::openssl_stream::client);
    std::cerr << ec.message() << std::endl;
}

Rendered as system:167772294: Unknown error 167772294.

The proper way would be creating an OpenSSL error category. For example:
https://github.com/chriskohlhoff/asio/blob/master/include/asio/ssl/impl/error.ipp

Note that there are some codes that actually are system codes:
https://github.com/boostorg/mysql/blob/4558bb4579ddd2a8eef8f2196e33f17b68c19506/include/boost/mysql/impl/internal/sansio/csha2p_encrypt_password.hpp#L39-L67