[fine] Many test improvements, error improvements

- Check for more error conditions
- Move to more definitive error assertions
- Simpler error messages in some cases
- Test more conditions more thoroughly, revisit old tests

fine/tests/expression/generic_function.fine

@@ -6,6 +6,6 @@ fun test() {
   generic_add(10, 10)
 }
 
-// @ignore
+// @ignore Feature is undesigned, this is tentative garbage
 // @no-errors
 // @eval: 20