Add abstract TransportFactory

[ozobotnovako]

Hi @mosquito , this PR aims to add an (optional) abstract TransportFactory letting users to implement alternative transports.

This PR is an alternative to #197 that brings less changes and is (hopefully) easier to merge.

[ozobotnovako]

Hi @mosquito, have you had a chance to take a look on this, please? Is there something I can do to get this merged? In case you are not interested in this feature or you don't have time to do the review, I'll just close this to clean up the PR log.

[mosquito]

Sorry, this PR happened during my big move and got lost in the mail. Let's discuss everything in the comments to code-review

[ozobotnovako]

Thanks for your comments @mosquito .

You are right with the is_ssl_url unclear purpose. Originally I made it this way to know when to create the SSL context in the connection object, but I have created SSLContextProvider instead. I also split the TCP and TLS factories as suggested.

I just wish I could add some tests that would use a different protocol such as udp, or tcp with inverse data, however this would require a proxy code that would convert the traffic back, so I'm not sure this is worth it.

[ozobotnovako]

@mosquito , I have fixed the linter error. Could you please re-run the workflow?