change `type Foo = string` to `type Foo string` for strict type checking

```console
$ git grep -n '^type .* = ' | grep -v '.pb.go'
pkg/downloader/downloader.go:41:type Status = string
pkg/guestagent/sockets/sockets.go:10:type Kind = string
pkg/guestagent/sockets/sockets.go:20:type State = byte
pkg/instance/start.go:391:type watchHostAgentEventsTimeoutKey = struct{}
pkg/instance/start.go:399:type launchingShellKey = struct{}
pkg/limatype/lima_instance.go:15:type Status = string
pkg/limatype/lima_yaml.go:77:type CPUType = map[Arch]string
pkg/limatype/lima_yaml.go:171:type SFTPDriver = string
pkg/limatype/lima_yaml.go:232:type ProvisionMode = string
pkg/limatype/lima_yaml.go:271:type ProbeMode = string
pkg/limatype/lima_yaml.go:285:type Proto = string
pkg/networks/usernet/config.go:18:type SockType = string
pkg/sshutil/format.go:15:type FormatT = string
```

`type Foo = string` should be changed to `type Foo string` so that type checking can be enforced on compilation

Start with the provided git grep results and inspect the type declarations in pkg/downloader/downloader.go, pkg/guestagent/sockets/sockets.go, pkg/instance/start.go, pkg/limatype/*.go, pkg/networks/usernet/config.go, and pkg/sshutil/format.go. Convert the listed aliases to defined types, then verify that the project compiles and type checking is enforced.

Written by the indexing model from the issue text.