Implement verifer stats parser

[aibor]

With ebpf.LogLevelStats the verifier outputs stats about the verification process. It would be nice to have a parser that provides the metrics as a dedicated data structure.

Up to now the format was quite stable. Although it was introduced with the note that "the format is expected to change in the future", it hasn't changed since it was added. Even if it changes in the future, it would be possible to support multiple formats.

The kernel bpf selftests have a parser for those stats. It would be easy to adapt it: a separate helper function that takes a verifier log string and outputs a dedicated stats data structure.

Would you be open to accept a PR for such a verifier stats parser? If so, where would be the best place for it? Should it be added to prog.go?