parseutil: cut dependency on go-sockaddr

**Is your feature request related to a problem? Please describe.**
`parseutil` brings [`go-sockaddr`](https://pkg.go.dev/github.com/hashicorp/go-sockaddr) just for two symbols ([SockAddrMarshaler](https://pkg.go.dev/github.com/hashicorp/go-sockaddr#SockAddrMarshaler) and [NewSockAddr](https://pkg.go.dev/github.com/hashicorp/go-sockaddr#NewSockAddr)) in `ParseAddrs`.

But this brings the full dependency tree of `go-sockaddr` into the dependency tree.

**Describe the solution you'd like**
`parseutil` should have the minimum dependencies. Move parsing code from go-sockaddr into parseutil.

**Describe alternatives you've considered**
https://github.com/hashicorp/go-sockaddr/issues/49