fix(knex)!: scope KnexQueueSchemaService to the driver module

[gerardp]

Closes #24.

Problem

The root barrel exported QueueSchemaService, whose constructor signature is
constructor(connection: Knex). That single export was the only reason the generated root
declaration file imported knex:

// build/index.d.ts
import { Knex } from 'knex'   // line 4

Since knex is an optional peer dependency, any consumer type checking with
skipLibCheck: false had to install it — even when using the Kysely, Redis or Sync adapter,
or a custom Adapter.

Change

Two commits, in the order they are easiest to read:

1. fix(knex)! — the export moves next to the adapter that needs it, mirroring what the
   Kysely module already does at src/drivers/kysely_adapter.ts:17.
2. refactor(knex)! — the class is renamed KnexQueueSchemaService and its file
   src/services/knex_queue_schema.ts, so the two driver modules are symmetrical and neither
   one holds the unqualified name.

// src/drivers/knex_adapter.ts
export { KnexQueueSchemaService } from '../services/knex_queue_schema.js'

Consumers now import it the same way they already import the Kysely equivalent:

import { knex, KnexQueueSchemaService } from '@boringnode/queue/drivers/knex_adapter'

The class body is untouched, and nothing changes at runtime. Updated along with it: the README's
two examples (plain Knex and the AdonisJS migration), the three test suites that construct it,
and the dedup guidance in the KnexAdapter error message, which now names
KnexQueueSchemaService.addDedupColumns().

The second commit is independent — drop it if you would rather keep the name as it is.

Verification

After yarn build, from 'knex' appears in exactly one declaration file, the one that owns the
dependency:

$ grep -rl "from 'knex'" build --include='*.d.ts'
build/src/drivers/knex_adapter.d.ts

End to end with the reproduction from the issue — npm pack of this branch, installed in a
clean project with typescript@7.0.2 and @types/node@25.9.4:

scenario	npx tsc --noEmit
published 0.7.1, root import, no knex installed	build/index.d.ts(4,22): error TS2307: Cannot find module 'knex'
this branch, root import, no knex installed	clean
this branch, KnexQueueSchemaService from the driver subpath with knex installed, including a createJobsTable call with an extend callback	clean

yarn typecheck, yarn lint and yarn format are clean (the two oxlint warnings in
src/otel.ts and tests/sync_adapter.spec.ts are pre-existing on main).

Note on the breaking change

This removes QueueSchemaService from the package root and renames it, so it is breaking for
anyone importing it today; the upgrade is a one-line import change. The alternative mentioned in
the issue — keeping the root export and typing the constructor structurally to drop the
import { Knex } — avoids the break but leaves the export in a barrel it does not belong to.
Happy to switch to that version if you would rather not break the current release line.

[gerardp]

Went ahead with the rename I asked about in the description: the schema service is now KnexQueueSchemaService in src/services/knex_queue_schema.ts, symmetrical with the Kysely module. It is a separate second commit, so it can be dropped if you would rather keep the current name — the packaging fix stands on its own in the first one.