use same lookup for mx-servers

[phoet]

this is built on the changes from #283 but instead of caching the result, we use the same lookup as with the regular disposable list. this results in a lookup from a set instead of iterating over the domains. this should be much faster overall and also removes the necessicty to do any caching.

[jurajjuricic-st]

Thanks, this works great!

[nijikon]

@phoet In this PR, you replaced mx_server_is_in? with disposable_mx_server?. Adding a note about this in the CHANGELOG would be a good idea, as the testing stub needs to be adjusted. https://github.com/micke/valid_email2?tab=readme-ov-file#test-environment

What do you think?

[phoet]

@nijikon i'm a new contributor and my knowledge does not strech the whole project yet. did you run into any trouble with the change? is there something we need to take care of that needs fixing?

i'm about to propse a change where all testing stubs can be replaced by an injected dns test stub. i found the current stubbing to be extremely cluttered and inconvenient to work with. i will definitively add a note to the changelog for that.

[nijikon]

Currently, if you use 7.0.11 along with the suggested stub from the documentation, you will encounter this error.

Failure/Error: allow_any_instance_of(ValidEmail2::Address).to receive_messages(valid_mx?: true, valid_strict_mx?: true, mx_server_is_in?: false)
          ValidEmail2::Address does not implement #mx_server_is_in?

[phoet]

@nijikon 7.0.12 should be there