Add checkstyle rules

[nielspardon]

I noticed we have cases where constructors are defined in the middle of a class.
https://github.com/substrait-io/substrait-java/pull/645/files#r2675549594

Typically, constructors should be defined towards the top of a class before any methods though after any fields. This is part of the Google Java styles we have adopted and can be enforced/checked using Checkstyle: https://checkstyle.sourceforge.io/google_style.html