Prevent duplicate Quick Edit save requests

[ArkaPrabhaChowdhury]

Fixes #25696

What changed

• Ignore repeated post and taxonomy Quick Edit saves while the current AJAX request is active.
• Clear the guard when the request completes, including failed requests.
• Add QUnit coverage for both editors.

Why

Double-clicking Quick Edit can submit duplicate requests. The first response removes the inline-edit row, while the second response then operates on missing markup.

Validation

• QUnit tests pass.
• JavaScript coding standards pass.
• JavaScript type checking passes.
• Built-files check passes.
• PHP coding standards checks pass in CI.

Trac: https://core.trac.wordpress.org/ticket/25696

[github-actions]

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