util: Abort on failing CHECK_NONFATAL in debug builds

This requires adjusting some tests to force exceptions over aborts, or
accept either exceptions or aborts.

Also, remove a fuzz test in integer.cpp that is mostly redundant with
the unit test added in the prior commit.

src/test/fuzz/integer.cpp

@@ -255,9 +255,4 @@ FUZZ_TARGET(integer, .init = initialize_integer)
         } catch (const std::ios_base::failure&) {
         }
     }
-
-    try {
-        CHECK_NONFATAL(b);
-    } catch (const NonFatalCheckError&) {
-    }
 }