Make the ring solver work in more situations

[felixwellen]

This PR contains two small upgrades/fixes for the ring solver:

• Adapt the approach from the monoid solver in the stdlib and also match structure which has the same normal form as the record field names of CommRingStr
• Allow the argument of the solver macro to be more things - so far only a variable of type CommRing worked...

[kangrongji]

Maybe it's not the best place to ask... I've got problem when I applied ring solver to integers and put the question as this message on Agda Zulip. Do you know what the problem is? @felixwellen

[felixwellen]

To repeat what has been said on zulip here: This problem is now also fixed by the PR.