This is a non functional change which consolidates the various packages
under metrics into the top level package now that the dead code is
removed.
It is a precursor to the removal of Victoria metrics after which all
erigon metrics code will be contained in this single package.
ergon/metrics contains a lot of unused types - the pull is removing them
prior to rationalizing between Prometheus and Victoria Metrics types.
It also have upgrades of golang-lru + sets types to v2 when possible.
