feat: add schedule source for psqlpy and aiopg

[danfimov]

closes #16 and #15

[Copilot]

Pull Request Overview

This PR adds schedule source functionality for PostgreSQL-based TaskIQ brokers, supporting both psqlpy and aiopg database adapters alongside the existing asyncpg implementation. The implementation allows for persistent storage and retrieval of scheduled tasks from PostgreSQL databases.

• Implements PSQLPyScheduleSource and AiopgScheduleSource classes with full CRUD operations for task schedules
• Refactors existing AsyncpgScheduleSource to inherit from a new shared base class BasePostgresScheduleSource
• Adds comprehensive integration tests covering all three database adapters

Reviewed Changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tests/integration/test_schedule_source.py	Integration tests for all three schedule source implementations
src/taskiq_pg/psqlpy/schedule_source.py	PSQLPy-based schedule source implementation
src/taskiq_pg/psqlpy/queries.py	SQL queries for PSQLPy schedule operations
src/taskiq_pg/psqlpy/init.py	Export PSQLPyScheduleSource in public API
src/taskiq_pg/asyncpg/schedule_source.py	Refactored to use shared base class
src/taskiq_pg/aiopg/schedule_source.py	Aiopg-based schedule source implementation
src/taskiq_pg/aiopg/queries.py	SQL queries for aiopg schedule operations
src/taskiq_pg/aiopg/init.py	Export AiopgScheduleSource in public API
src/taskiq_pg/_internal/schedule_source.py	Shared base class for PostgreSQL schedule sources
src/taskiq_pg/_internal/init.py	Export shared base class
pyproject.toml	Linting configuration updates

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