Tests: Add unit test for pagination trailing slash

[Infinite-Null]

Trac ticket: #61393

Description

Adds a unit test to verify pagination links maintain consistent trailing slash behavior when the permalink structure has trailing slash as well as does not have trailing slash.

Testing instructions

1. Run the unit test:

npm run test:php -- --filter=test_pagination_links_trailing_slash_consistency

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[Infinite-Null]

I have updated the implementation to address the failing test cases.