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/fetch.go

@@ -17,8 +17,8 @@ import (
 	"github.com/mjl-/bstore"
 
 	"github.com/mjl-/mox/message"
+	"github.com/mjl-/mox/mox-"
 	"github.com/mjl-/mox/moxio"
-	"github.com/mjl-/mox/moxvar"
 	"github.com/mjl-/mox/store"
 )
 
@@ -102,7 +102,7 @@ func (c *conn) cmdxFetch(isUID bool, tag, cmdstr string, p *parser) {
 				p.xspace()
 				changedSince = p.xnumber64()
 				// workaround: ios mail (16.5.1) was seen sending changedSince 0 on an existing account that got condstore enabled.
-				if changedSince == 0 && moxvar.Pedantic {
+				if changedSince == 0 && mox.Pedantic {
 					// ../rfc/7162:2551
 					xsyntaxErrorf("changedsince modseq must be > 0")
 				}