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.

go.mod

@@ -4,7 +4,6 @@ go 1.25
 
 require (
 	github.com/anacrolix/log v0.17.1-0.20251118025802-918f1157b7bb
-	github.com/anacrolix/missinggo/v2 v2.10.0
 	github.com/anacrolix/torrent v1.61.0
 	golang.org/x/sys v0.38.0
 	golang.org/x/term v0.37.0
@@ -22,6 +21,7 @@ require (
 	github.com/anacrolix/go-libutp v1.3.2 // indirect
 	github.com/anacrolix/missinggo v1.3.0 // indirect
 	github.com/anacrolix/missinggo/perf v1.0.0 // indirect
+	github.com/anacrolix/missinggo/v2 v2.10.0 // indirect
 	github.com/anacrolix/mmsg v1.0.1 // indirect
 	github.com/anacrolix/multiless v0.4.0 // indirect
 	github.com/anacrolix/stm v0.5.0 // indirect