Provide type hint code lenses for instance methods

Similar to the Haskell language server:


We might want to disable the 'apply' command, since explicit method type signatures are not valid Curry syntax.

Start by examining the existing code-lens entry point and the handling of the “apply” command, using the Haskell language server behavior as a reference. Determine how instance methods are identified and how Curry syntax limits explicit method type signatures. Done means providing type hint code lenses for instance methods and disabling “apply” where it would produce invalid Curry syntax.

Written by the indexing model from the issue text.