Do not print unexpected attributes to console

[hendrikvanantwerpen]

TSSG prints warnings to the console if nodes have unexpected attributes defined on them. Printing to the console from a library is bad practice and can break applications using the library. (For example, LSP is often implemented over and stdio connection, and unexpected output breaks that.)

Instead of printing the warnings, we should return them as part of the result, and leave processing them up to the caller.