Use milliseconds everywhere

discussion: maybe we should use milliseconds everywhere in metrics

_Originally posted by @wemeetagain in https://github.com/ChainSafe/lodestar/pull/8838#discussion_r2829328302_

To clarify, I think we should use milliseconds but when passing values to metrics we need to use seconds (prometheus best practices) and all our metrics are `_seconds`. It would be good if this can be handled internally by our metric register, ie. caller passes as milliseconds and it gets converted to seconds internally.