enhancement: add postgres support

[jasonmccallister]

Adds postgres support, as default, with a new createQueue factory helper. PostgreSQL driver run migrations

[Copilot]

Pull request overview

This PR introduces a pluggable driver architecture for @snaapi/queue and adds a new Postgres-backed implementation (now the default when using the new createQueue() factory), with accompanying docs, tests, and CI updates.

Changes:

• Introduces a QueueDriver interface and refactors the queue/worker/dispatcher/middleware pipeline to be backing-store agnostic (Deno KV and Postgres).
• Adds a Postgres driver (schema/migrations, LISTEN/NOTIFY + polling consumer, locks/counters/failed-job storage).
• Adds Postgres integration tests, Docker compose setup, and CI job configuration to run both KV and Postgres test suites.

Reviewed changes

Copilot reviewed 19 out of 20 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tests/queue_test.ts	Updates job context assertions to validate locks/counters instead of kv.
tests/postgres_test.ts	Adds Postgres integration test suite covering dispatch, delay, context, middleware, chains, uniqueness, failed jobs, retries, and migrations.
src/worker.ts	Refactors worker execution to use QueueDriver and populates JobContext with locks/counters.
src/types.ts	Updates JobContext to expose locks/counters primitives; updates comments around backing store.
src/queue.ts	Makes Queue accept Deno.Kv or QueueDriver, adds listener lifecycle management, and exposes driver.
src/middleware.ts	Migrates rateLimit / withoutOverlapping from direct KV usage to ctx.counters / ctx.locks.
src/failed.ts	Refactors FailedJobStore into a driver-backed facade.
src/factory.ts	Adds createQueue() factory selecting driver via env/options (defaults to Postgres).
src/drivers/types.ts	Introduces driver interfaces: enqueue/listen/unique, failed store, locks, counters.
src/drivers/postgres.ts	Adds Postgres driver: schema/migrate, enqueue, LISTEN/NOTIFY listener loop, locks/counters/failed store.
src/drivers/deno-kv.ts	Adds Deno KV driver implementing the new driver interfaces.
src/dispatcher.ts	Refactors dispatcher to enqueue through QueueDriver (including unique dispatch).
src/chain.ts	Refactors chain dispatch/advance to use QueueDriver.
scripts/migrate.ts	Adds a script to run Postgres schema migration from the CLI.
mod.ts	Exports the new factory and drivers/types.
deno.lock	Adds npm:pg dependency.
deno.json	Adds imports mapping for pg and adds tasks for Postgres testing and DB lifecycle/migration.
compose.yaml	Adds local Postgres service definition for development/testing.
README.md	Updates docs to describe backing stores, createQueue(), Postgres usage, and migration notes.
.github/workflows/ci.yml	Adds Postgres service and runs both KV and Postgres test tasks in CI.

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