Adds a regression test ensuring `sort_maps` only sorts map keys, not
sequence values. The bug in #876 sorted all `Seq` values (including
`Vec`), which broke snapshot stability for ordered collections.

The test snapshots a `HashMap` containing a `Vec` with `sort_maps`
enabled and asserts the Vec order is preserved.

> _This was written by Claude Code on behalf of max-sixty_

---------

Co-authored-by: Claude <noreply@anthropic.com>

The Arc→Rc change (#873) and Send+Sync removal (#874) were
semver-breaking — they removed auto-trait impls from `Settings`,
`Redactions`, `Redaction`, and `SettingsBindDropGuard`. This broke
downstream crates like
[cedar-policy](cedar-policy/cedar-spec#917)
that depend on `Send + Sync`.

This reverts to `Arc` and restores `Send + Sync` bounds on `Redaction`
and `dynamic_redaction()`. Also adds `Send + Sync` to the `Comparator`
trait (new in 1.47.0) since `Arc<ActualSettings>` requires it. A
compile-time assertion prevents future regressions.

TODOs mark the `Arc` usage and `Comparator` bounds as candidates for
removal in the next breaking change.

Thanks to @john-h-kastner-aws for reporting in #873 (comment).

> _This was written by Claude Code on behalf of @max-sixty_

Co-authored-by: Claude <noreply@anthropic.com>

Patch release restoring `Send + Sync` on `Settings`, `Redactions`, and
`Redaction` after the semver-breaking change in 1.47.0.

Follow-up to #893.

> _This was written by Claude Code on behalf of @max-sixty_

---------

Co-authored-by: Claude <noreply@anthropic.com>