server::listener: provide method for catching binding errors

[Tectu]

As of today, malloy::server::listener binds starts to listen in the constructor. If the acceptor could not start listening (for example because the end-point is already in use), there is no way for a consumer to catch this programmatically.

Possible solutions:

• Throw in the constructor (meh)
• Move relevant pieces of code from constructor to run() and return boolean.