toString

Reproduces the data-class text YorkieException(code=…, errorMessage=…) for a plain YorkieException — a hard-coded literal, NOT javaClass.simpleName, so the base class's own name stays byte-identical to the pre-open-class data-class output even under R8 minification in a consumer app with no keep rule for it (a review finding on the change apply error: javaClass.simpleName alone is not R8-stable). A subclass — e.g. ChangeApplyError(code=…, errorMessage=…) — still uses Any.javaClass/Class.getSimpleName, so its OWN name can be obfuscated by R8 in a consumer app without a keep rule for that subclass; a consumer-rules follow-up (e.g. a -keep entry, or extending the literal approach to subclasses) is intentionally not added here, out of this fix's scope.