expose fewer internals in packages, for easier software reuse

- prometheus is now behind an interface, they aren't dependencies for the
  reusable components anymore.
- some dependencies have been inverted: instead of packages importing a main
  package to get configuration, the main package now sets configuration in
  these packages. that means fewer internals are pulled in.
- some functions now have new parameters for values that were retrieved from
  package "mox-".

imapserver/server.go

@@ -1456,7 +1456,7 @@ func (c *conn) cmdStarttls(tag, cmd string, p *parser) {
 		panic(fmt.Errorf("starttls handshake: %s (%w)", err, errIO))
 	}
 	cancel()
-	tlsversion, ciphersuite := mox.TLSInfo(tlsConn)
+	tlsversion, ciphersuite := moxio.TLSInfo(tlsConn)
 	c.log.Debug("tls server handshake done", slog.String("tls", tlsversion), slog.String("ciphersuite", ciphersuite))
 
 	c.conn = tlsConn