[PM-30267] fix(importer): preserve protected KeePass custom fields as hidden fields

[majiayu000]

Summary

• Protected fields (ProtectInMemory="True") are now always imported as hidden custom fields
• Previously, long (>200 chars) or multiline protected fields were appended to notes instead

Fixes #16897

Test plan

• Import KeePass V2 XML with protected custom fields
• Verify protected fields appear as hidden custom fields (not in notes)
• Verify this works for short, long, and multiline protected values

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[bitwarden-bot]

Thank you for your contribution! We've added this to our internal tracking system for review.
ID: PM-30267
Link: https://bitwarden.atlassian.net/browse/PM-30267

Details on our contribution process can be found here: https://contributing.bitwarden.com/contributing/pull-requests/community-pr-process.

[harr1424]

Hi @majiayu000 👋 !

Thanks for another valuable contribution!

This link describes](https://contributing.bitwarden.com/contributing/pull-requests/community-pr-process/) the process that your contribution will undergo before becoming a part of the Bitwarden codebase. Please keep in mind that your submission will be reviewed by Bitwarden's product and engineering teams before an official code review happens on Github. Since this review process occurs internally, it may seem as though little progress is taking place.

Thank you for your patience throughout the review process, and please feel free to check in at anytime by tagging me here.

[majiayu000]

Thanks for the update! I understand the process and will be patient. Feel free to reach out if you need any changes or have questions about the implementation.