Fix OTP input truncating when pasting (with separator)

[sondr3]

Description

Fix pasting into OPT input truncating last input:

Screen.Recording.2026-07-30.at.17.19.49.mov

Motivation & Context

I mentioned this in the v6 forms discussion, but this has been bugging me for so long I decided to fix it myself. If you checkout the first commit (434e36f652a747b8d5b5f9182486e1b12083a878) the test will fail because of this bug.

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-42939--twbs-bootstrap.netlify.app/

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