perf(Storage/Local): avoid recursive array_merge in searchInDir

[joshtrichards]

• Resolves: #

Summary

searchInDir():

• Refactors traversal to avoid recursive array_merge accumulation overhead.
  • Less expensive on large trees
• Also tightens search traversal behavior around symlinks when symlinks are disallowed.
  • symlink-related behavior is even stricter when symlinks are disabled now.

Also refactors file_exists():

• Extracts case-insensitive exact-case (yes) existence logic into a dedicated helper.
• Documents why exact basename lookup is required when localstorage.case_insensitive is enabled (hint: case-only rename/copy correctness).

TODO

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI