Download the appropriate file with `wasmer package download`

[ayys]

When downloading a package release from the CLI, currently it fetches whatever url is in webcUrl field. This means sometimes, the requested package hash and the downloaded file's hash can mismatch. Reason being, if the user specifies the hash of a webcv2, the downloaded file will be webcv2 still.

To fix, check the hash and download the appropriate file (webcv2 or webcv3).