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-".

smtp/address.go

@@ -7,9 +7,11 @@ import (
 	"strings"
 
 	"github.com/mjl-/mox/dns"
-	"github.com/mjl-/mox/moxvar"
 )
 
+// Pedantic enables stricter parsing.
+var Pedantic bool
+
 var ErrBadAddress = errors.New("invalid email address")
 
 // Localpart is a decoded local part of an email address, before the "@".
@@ -262,7 +264,7 @@ func (p *parser) xlocalpart() Localpart {
 		}
 	}
 	// In the wild, some services use large localparts for generated (bounce) addresses.
-	if moxvar.Pedantic && len(s) > 64 || len(s) > 128 {
+	if Pedantic && len(s) > 64 || len(s) > 128 {
 		// ../rfc/5321:3486
 		p.xerrorf("localpart longer than 64 octets")
 	}