feat: Add PaginatedRequestQuery schema for reusable query parameters (#258)

[doubledare704]

• Created PaginatedRequestQuery Pydantic model in fastcrud/paginated/schemas.py

  • Encapsulates all pagination query parameters (offset, limit, page, items_per_page, sort)
  • Includes comprehensive docstring with usage examples
  • Supports both page-based and offset-based pagination modes
  • Uses Field descriptions for OpenAPI documentation
  • Configured with populate_by_name for alias support

• Refactored _read_items endpoint in fastcrud/endpoint/endpoint_creator.py

  • Now uses PaginatedRequestQuery with Depends() instead of individual Query parameters
  • Maintains backward compatibility with existing API behavior
  • Updated docstring to mention the new schema-based approach

• Updated fastcrud/paginated/init.py to export PaginatedRequestQuery

• Added comprehensive tests in tests/sqlalchemy/paginated/test_schemas.py

  • Tests for default values, pagination params, offset/limit, sorting
  • Tests for alias support and populate_by_name configuration
  • All 15 tests passing

• Added reusability tests in tests/sqlalchemy/endpoint/test_paginated_request_query_reusability.py

  • Demonstrates using PaginatedRequestQuery in custom endpoints
  • Tests OpenAPI schema generation
  • Tests subclassing capability for custom extensions
  • All 10 tests passing

• Updated documentation in docs/advanced/endpoint.md

  • Added new section 'Reusing Pagination Query Parameters'
  • Includes examples of using PaginatedRequestQuery in custom endpoints
  • Shows how to extend the schema with custom parameters
  • Documents benefits of using the schema

Resolves #258

Checklist

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• I have added necessary documentation (if appropriate).
• I have added tests that cover my changes (if applicable).
• All new and existing tests passed.

Additional Notes

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