Re-export WithSafeHTTP, WithHTTPClient, WithTransport at package root

[andrew]

v0.6.0 added client.WithSafeHTTP, client.WithHTTPClient, and client.WithTransport, but registries.go only re-exports WithTimeout and WithMaxRetries alongside NewClient/Option.

Consumers that already use registries.NewClient(...) have to add a second import of github.com/git-pkgs/registries/client just to reach the new options. Adding

var WithSafeHTTP = client.WithSafeHTTP
var WithHTTPClient = client.WithHTTPClient
var WithTransport = client.WithTransport

next to the existing WithTimeout/WithMaxRetries vars would keep the top-level surface consistent.

Noticed while wiring WithSafeHTTP into enrichment.