Extend GET pagination endpoints with max default offset

[codesungrape]

Description

Trello card: https://trello.com/c/dRDnYYYO
This PR introduces a configurable maximum offset value for pagination across reservation endpoints.

• Adds a MAX_OFFSET environment variable with a fallback default of 2000.
• Ensures offsets cannot exceed this maximum; otherwise, a validation error is raised.
• Default offset remains 0 for normal pagination use.
• Cleans up redundant offset validation logic and tests.

Fixes # (issue number if applicable)

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• Added unit tests for invalid offset values (negative, above max).
• Updated reservation service and controller tests to validate new logic.
• Verified default behavior when no MAX_OFFSET is provided.
• Ran full test suite – all tests passing.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My individual commit messages are descriptive and follow our commit guidelines
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[Copilot]

Pull Request Overview

This PR implements a configurable maximum offset value for pagination across book and reservation GET endpoints. It adds validation to ensure offset values cannot exceed a configurable maximum while maintaining the default behavior for normal pagination.

• Adds MAX_OFFSET configuration with environment variable support and 5000 default fallback
• Implements offset validation logic in both books and reservations endpoints
• Updates test coverage to validate the new offset range restrictions

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
app/config.py	Adds MAX_OFFSET configuration with safe integer parsing and fallback default
app/routes/legacy_routes.py	Implements offset validation against MAX_OFFSET in books endpoint
app/routes/reservation_routes.py	Implements offset validation against MAX_OFFSET in reservations endpoint
tests/test_pagination.py	Adds test coverage for out-of-range offset validation in books endpoint
tests/test_reservations.py	Adds test coverage for out-of-range offset validation in reservations endpoint
tests/conftest.py	Removes debug print statement

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