Protobuf conformance: add test cases for protojson non-numeric int/float parsing

We got a bug report for Go Protobuf where users discovered that in Go Protobuf,
parsing does not fail despite trailing garbage after numbers:
related to https://github.com/golang/protobuf/issues/1678

Let’s add these cases to the conformace test suite to ensure consistent behavior
across the various Protobuf implementations.

PiperOrigin-RevId: 853056737