Adds a case telling shallow from deep history

[johnnyt]

Refs: st-1wy4

What this adds

The loan chart's history h is shallow, but every child of active it can
remember is a leaf, so shallow and deep history restore the same
configuration: changing type="shallow" to type="deep" left every case
agreeing. A shallow history differs from a deep one only when the remembered
child is compound.

loan_dispute_restores_late_shallowly is a new case pair under
conformance/cases/library/. Its loan chart is the one the other loan cases
use, with due_soon and overdue gathered under a compound late state
(initial due_soon), so the child of active that h remembers is
compound. The loan goes due-soon, then overdue (which sends the lost-item
timer), a dispute takes it out of active, and the resolution re-enters
late through h at its initial due_soon, not at overdue; the
lost-item timer is sent once. It uses only the conformance README's
library-world events, ids and durations, and registers both send types,
library:timer then library:route.

The mutation check

With the history's type changed from shallow to deep in the new chart
(the file copied first), mix test.baseline add refused the case and left
the ratchet unchanged, and running it through the corpus runner reported
the disagreement at the resolution step: expected due_soon, got
overdue. The file was restored from the copy and compared byte-equal with
cmp; the case then agreed again.

What moved in the corpus

• test/passing_tests.json gains the case (through mix test.baseline add,
  which ran it first).
• conformance/corpus/statifier.json, conformance/manifest.json and
  conformance/registry.json are regenerated by mix statifier.corpus: the
  statifier suite's case_count goes from 35 to 36, the registry claims the
  new case, and corpus_hash moves. A sibling that vendors the corpus
  re-vendors at the next tag.
• The scion and w3c corpus files and exclusions.json were rewritten by the
  emitter with no change, from an upstream tree transformed in this branch's
  worktree with the current stylesheet.

No changelog fragment (changelog.d/README.md excludes conformance
fixtures).

Gate

Full mix quality (mix gate.verify) green on this commit's tree after the
rebase onto the current main, and the merge profile
(mix quality --profile merge) green, the ADR judge skipped because no file
is in a judged scope.

Review

Tier: gate (conformance fixtures and generated files). The in-turn review of
the diff found nothing blocking; its two advisories (the case does not go on
to fire loan.lost from the restored state, and the chart keeps the loan
datamodel and renewal transition it does not exercise, as the sibling loan
cases do) were left as they are.