Checker report only one message per no safe type

[marcosbracco]

Currently checker reports one error message each time a non-safe type is used.
It will be more user readable to report one error message for each type

[marcosbracco]

Done, checker has now a cache of already verified types, for each kind of verification a type may require. This makes things go a little faster (no need to re check every type) and also allows reporting the full error detail only one time, other instances of the same error get reported in a single line without details. This makes the console log easier to dive when there are many errors.