all: cut bloat found in the pike audit

Dead, vestigial, and over-built code with no behavior change (except the
bool-vocabulary trim, a deliberate behavior tightening):

- httpdl: drop the vestigial sort+copy in validSegs (work-stealing was
  removed in 270812d, so segments always tile [0,total) ascending now);
  validate order in place, which also rejects a scrambled sidecar. Inline
  the endOff() accessor to s.end.
- cli: shrink the boolean vocabulary to true/false, which is all that's
  accepted. The invented yes/no/1/0/on/off spellings are gone, so e.g.
  --enable-dht=yes (or yes in got.conf) is now a usage error.
- download: remove the dead, never-called Stat.Done() method.
- progress: drop speed(), a pure alias of humanSize; call humanSize directly.
- main: replace the jobsHolder mutex box with atomic.Pointer[[]job] for the
  forced-exit session save; the capability stays, the lock and type go.
- bt: collapse isAddrInUse's X||X (missinggo.IsAddrInUse is that exact
  string match); drop the now-unused missinggo import (tidy -> indirect).
- option: note that prealloc and falloc are identical here.

bt/bt.go

@@ -19,7 +19,6 @@ import (
 	"time"
 
 	alog "github.com/anacrolix/log"
-	missinggo "github.com/anacrolix/missinggo/v2"
 	"github.com/anacrolix/torrent"
 	"github.com/anacrolix/torrent/metainfo"
 	"github.com/hanbok/got/download"
@@ -172,10 +171,11 @@ func NewClient(cfg ClientConfig) (*torrent.Client, error) {
 	return cl, nil
 }
 
-// isAddrInUse reports whether err is an "address already in use" bind failure,
-// matching either missinggo's helper or the raw string the library wraps.
+// isAddrInUse reports whether err is an "address already in use" bind failure.
+// (anacrolix/missinggo's IsAddrInUse is this exact string match, so we just do
+// it directly rather than carry the import for it.)
 func isAddrInUse(err error) bool {
-	return err != nil && (missinggo.IsAddrInUse(err) || strings.Contains(err.Error(), "address already in use"))
+	return err != nil && strings.Contains(err.Error(), "address already in use")
 }
 
 // Options are the per-download settings.