fix: *_and_log and log no longer raise Ecto.ConstraintError on audit_logs_pkey (on_conflict: :nothing)

[palantir-valiot]

Summary

Prevent Ecto.ConstraintError on audit_logs_pkey (unique) during best-effort audit logging in update_and_log / insert_and_log / upsert_and_log / delete_and_log / log by changing the internal repo.insert for the Changelog row to use on_conflict: :nothing, conflict_target: :id.

The audit log is intentionally best-effort (errors are logged and swallowed, the outer operation still succeeds). Duplicate log attempts (from retries, Multi re-entrancy, or pkey sequence skew under load) now silently no-op instead of raising inside the transaction and rolling back user work.

Also: version bump to 1.0.4, CHANGELOG entry, and refresh of allowed-range outdated deps (benchee 1.5.0→1.5.1, credo 1.7.18→1.7.19 + transitives).

Why

Stacktrace from OPS-4605 (eliot-lamosa-gto-prod):

(ecto_trail 1.0.3) lib/ecto_trail/ecto_trail.ex:435: EctoTrail.log_changes/5
(ecto_trail 1.0.3) lib/ecto_trail/ecto_trail.ex:315: anonymous fn/4 in EctoTrail.update_and_log/4
...
** (Ecto.ConstraintError) constraint error when attempting to insert struct:
    * "audit_logs_pkey" (unique_constraint)

Triage: NOTIFY+FIX, category code_bug. The root cause is a missing duplicate-log guard on the pkey insert of the audit row (table uses a plain serial/identity id pkey with no natural unique on (resource,resource_id,change_type,inserted_at) etc.).

Fix is minimal and localized to the two log_changes* helpers that perform the audit insert. No behavior change for happy path; only changes the error path from "raise and rollback" to "best-effort log + continue".

Test plan

• mix deps.get
• mix compile (clean; only pre-existing redundant-clause warning on map_custom_ecto_type)
• mix format --check-formatted (exit 0)
• mix hex.outdated + mix deps.update for allowed updates (benchee, credo) — now all up-to-date within constraints
• Read git diff (own diff) before commit — matches scope, no debug prints, no scope creep
• Added regression test exercising the pkey collision path (seed row + rewind sequence so internal insert hits unique violation; update_and_log still succeeds)
• mix test attempted (fails only on "connection refused" to Postgres in this agent pod; the new test and all prior *_and_log / Multi cases are present and would exercise the on_conflict path; CI with real DB will run it)
• Version bumped in mix.exs (1.0.3 → 1.0.4)
• CHANGELOG.md updated (concise one-line-per-change style)
• Branch name exactly palantir/OPS-4605-audit-log-pkey-unique-constraint
• One PR per task

Closes OPS-4605

[linear-code]

OPS-4605

[acrogenesis]

Closing as a duplicate of #24 — same bug: Ecto.ConstraintError on audit_logs_pkey in EctoTrail.log_changes/5. These were generated from a backlog of duplicate Linear issues created by a log-agent dedup gap (now fixed in palantir 38438d6; no new duplicates are being filed). Consolidating on #24.