Trait bounds for associated types (#40)

* Adds trait bounds based on used types

* Adds test

* Cleans up the code

* Cleans up the code, attempts to add spanned errors

* Fixes error reporting

* Adds non-encodable type to the test

* Apply suggestions from code review

Co-Authored-By: 0x7CFE <korvin@deeptown.org>

* Fix typo

Co-Authored-By: 0x7CFE <korvin@deeptown.org>