fix(netx): ensure we create ~same HTTP3 and HTTP2 transports

[bassosimone]

1. Use the netxlite.NewHTTPTransport factory for creating a new
   HTTP2 (and HTTP1) transport;

2. Recognize the netxlite.NewOOHTTPTransport has now become
   an implementation detail so make it private;

3. Recognize that netxlite.NewHTTP3Transport should call
   netxlite.WrapTransport so it returns the same typechain
   returned by netxlite.NewHTTPTransport (modulo, of course,
   the real underlying transport), so ensure that we are
   calling netxlite.WrapTransport in NewHTTP3Transport;

4. Recognize that the table based constructor inside of
   netx needs a logger to create HTTPTransport instances using
   either netxlite.NewHTTP{,3}Transport so pass this argument
   along and ensure it's not nil using a constructor inside
   model that guarantees that;

5. Cleanup netx's tests to avoid type asserting on the
   typechains returned by netxlite since we already test
   that inside netxlite;

6. Recognize that now we can make more legacy names inside
   of netxlite private because we don't need to use them
   inside tests anymore (because of previous point).

Reference issue: ooni/probe#2121