chore(deps): update go toolchain directive to v1.26.3

See merge request !294

chore(deps): update golang docker tag to v1.26.3

See merge request !295

Introduce an outbox table to ensure at-least-once delivery of events. Create
the `event_outbox` table with necessary fields, including indexes for
polling unpublished and cleaning up old events. Implement the `WithOutbox`
option in the options.go file to toggle the outbox feature. Add initial
tests for the outbox processor to validate event publishing and error
handling scenarios. This enhances the system's reliability and consistency
in event processing.

Adds tests for the processEntry reconstruct-error path, the not-an-Event
reconstruct branch, StoreEvent's outbox-insert error, the cleanup ticker
firing, and the snapshot.When accessor. Exposes a configurable cleanup
interval to make the cleanup branch reachable from tests without
waiting an hour.

feat(outbox): add transactional outbox for reliable event publishing

See merge request !229

Adds new documentation for command idempotency, explaining its 
importance and implementation details. Introduces methods to ensure 
duplicate command executions return the original result, preventing 
data inconsistencies. Updates tests to include an additional row 
for coverage on idempotent commands.

feat(idempotency): postgres IdempotencyStore implementation

See merge request !297

Implement MetricsRecorder interface to allow tracking of 
PostgreSQL-specific metrics, including outbox operations and 
event loading. Introduce NoOpMetricsRecorder for no-op usage 
and integrate metrics recording in Store methods for enhanced 
monitoring and observability.

feat(metrics): postgres MetricsRecorder integration

See merge request !298

chore(release): prepare for v1.19.0

See merge request !296