v1.3.2

Follow-up on the v1.3.1 review-round batch — two spots the sweep still
missed.

• Fixed TestErrorStructSize (added in v1.3.1 to pin the 144 B layout
  fix) asserted 144 unconditionally, failing on any 32-bit target: uintptr
  and slice/string header words are 4 bytes there, and time.Duration
  (retryDelay) aligns to 4 rather than 8 — hand-computed and confirmed at
  80 B for GOARCH=386 (no 32-bit CI runner to run it on directly, but
  go vet/go test -c cross-compile cleanly). The test now branches on
  unsafe.Sizeof(uintptr(0)). Test-only; no library behavior changed on
  any platform.
• Docs Three more enumerations of the client-visible channels missed
  the retry delay: DESIGN.md's WithoutPublic edge-case-table row, the
  README "at the source" intro paragraph, and detailed's (format.go)
  internal comment on what %+v gathers.