fix: block prev pagination while another query is loading

[RaphaelFakhri]

Title: fix: block prev pagination while another query is loading

CLA

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• Code changes are tested

Description of the changes, What, Why and How?

BasePaginator.canExecuteQuery only checked isLoading for the next direction because of operator precedence: (!isLoading && next && hasNext) || (prev && hasPrev). Calling prev() twice quickly sent two requests with the same cursor, and both results were appended to items.

The isLoading check now applies to both directions. A test in BasePaginator.test.ts starts a prev() query, calls prev() again while it is in flight, and checks that only one query is dispatched. The test fails on the previous code (3 query calls instead of 2) and passes with this change.

Changelog

• Prevent duplicate prev page queries while a paginator is loading.