test: update trust anchor examples/fixtures for anchors array

[scouten-adobe]

Summary

PR contentauth/c2pa-rs#2545 replaces Trust.trust_anchors / Trust.user_anchors (both Option<String>) with Trust.anchors (Option<Vec<TrustAnchor>>), where each TrustAnchor carries trust_anchors, trust_uri, and trust_kind. This updates the remaining examples/fixtures that still use the old flat fields so they match the new schema once that PR lands:

• sdk/examples/c2pa.toml -- the commented-out [trust] template now shows [[trust.anchors]] instead of top-level trust_anchors/user_anchors. (Stays in contentauth/c2pa-rs -- sdk/ isn't part of this repo.)
• tests/fixtures/trust/cawg_sign_settings.toml and tests/fixtures/trust/cawg_test_settings.toml -- both used [trust] trust_anchors = "..." (the C2PA-level trust, not cawg_trust, which is a separate, unaffected struct); restructured to [[trust.anchors]] with trust_uri and trust_kind = "signer", matching the convention contentauth/c2pa-rs#2388 itself uses in sdk/tests/fixtures/test_settings.toml.

Test plan

• Verified all 3 files parse as valid TOML.
• Ran cargo test -p c2patool --test integration cawg against current main -- all 4 CAWG integration tests still pass (the unknown [[trust.anchors]] key is currently ignored, since main doesn't yet have the anchors field; this becomes load-bearing once fix: C2PA 2.3 reporting c2pa-rs#2388 merges).
• Re-verify once fix: C2PA 2.3 reporting c2pa-rs#2388 merges that these fixtures still produce a trusted validation result under the new schema.

---

Migrated from contentauth/c2pa-rs#2436 as part of the c2patool repo split. Only the two cli/tests/fixtures/trust/*.toml changes (now tests/fixtures/trust/*.toml) carried over here; the sdk/examples/c2pa.toml edit stays in the c2pa-rs PR.

[scouten-adobe]

Closing as superseded. This was migrated from contentauth/c2pa-rs#2436 during the c2patool repo split, but both fixture files it touches (tests/fixtures/trust/cawg_sign_settings.toml and tests/fixtures/trust/cawg_test_settings.toml) were independently and correctly migrated to the [[trust.anchors]] schema by contentauth/c2pa-rs#2545 before the split landed.

Merging this PR as-is would actually break settings parsing: it conflicts with main on cawg_sign_settings.toml, and both files use trust_kind = "signer", which no longer exists (#2545 named the enum variant manifest, not signer). I confirmed against current main:

ERR: unknown variant `signer`, expected one of `manifest`, `tsa`, `cawg`

I found and fixed the identical issue while resolving merge conflicts on the sibling PR, contentauth/c2pa-rs#2436. Nothing here needs to be carried forward.