Replacing the snews format checker

[KaraMelih]

With SNEWS2/SNEWS_Publishing_Tools#81 we are getting rid of the snews format checker, and instead validating the messages upon generation.

Previously we were using a script called snews format checker where the neutrino times, p values etc are checked for each message in a standalone script, and using the same script within the snews coincidence system to make sure that the message comes from snews pt and not a stray message injected into the stream -which might potentially crash the server if not ignored.

Now that we have gotten rid of that, we should either write something that checks the similar properties of each received message, or we can again use the snews_pt as a dependency and try to rebuild a new message and check if it self validates again.

I'm open to alternative suggestions.

[KaraMelih]

@sybenzvi this is the issue I was referring to. @justinvasel suggested to use Pydantic which we also had discussed in the past. It may now be a good time to reconsider it.

[KaraMelih]

to keep an eye on the issue, I mention it here.
Being worked at here; https://github.com/SNEWS2/snews-data-formats
@justinvasel