Add schedule source

[danfimov]

No description provided.

[Copilot]

Pull Request Overview

This PR adds schedule source functionality for task scheduling in PostgreSQL-backed TaskIQ implementations, introducing AsyncpgScheduleSource for persistent task scheduling and updating project documentation.

• Implements schedule source class with PostgreSQL storage for task schedules
• Adds documentation for schedule sources and common issues
• Updates broker validation logic and removes unused assignment

Reviewed Changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/taskiq_pg/asyncpg/schedule_source.py	New schedule source implementation with database operations
src/taskiq_pg/asyncpg/queries.py	Added SQL queries for schedule table operations
src/taskiq_pg/asyncpg/broker.py	Fixed broker startup validation logic
src/taskiq_pg/psqlpy/broker.py	Fixed broker startup validation logic
src/taskiq_pg/asyncpg/result_backend.py	Removed unnecessary assignment of deletion result
examples/example_with_schedule_source.py	Added example demonstrating schedule source usage
docs/	Updated documentation with schedule source tutorial and common issues

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