Fix StackOverflowError deleting a bookmark folder with a relation cycle

[Asgabani]

Summary

Fixes #5928.

RealSavedSitesRepository.traverseBranch() walked the bookmark folder tree via unbounded recursion, with no protection against a cycle in the relations table. If the relations table ever ends up with a folder cycle (corrupted/inconsistent data), traversal recurses forever and the app crashes with a StackOverflowError — matching the reported crash trace, which shows traverseBranch recursing repeatedly during a folder delete.

Fix

Replaces the recursive traversal with an iterative one (ArrayDeque + a visited-folder Set), so a folder that's already been visited is skipped instead of revisited indefinitely. Traversal order/output is unchanged for normal (acyclic) folder trees.

Test plan

• Added whenFolderRelationsContainACycleThenGetFolderBranchTerminatesWithoutDuplicates, which inserts a corrupted cyclic relation (folderA ↔ folderB) directly via the DAOs and asserts getFolderBranch terminates and returns each folder exactly once.
• Ran the full SavedSitesRepositoryTest suite (65 tests) — all pass, including every existing getFolderBranch/deleteFolderBranch test.
• spotlessApply run, diff is clean.

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Note

Low Risk
Localized change to private folder traversal with a regression test; behavior for valid trees is intended to stay the same while only corrupt cyclic data is handled differently.

Overview
Fixes #5928 by hardening bookmark folder branch traversal when the relations table contains a folder cycle (corrupted data), which previously caused unbounded recursion and a StackOverflowError during operations like folder delete that call getFolderBranch.

RealSavedSitesRepository.traverseBranch() is changed from recursive depth-first walking to an iterative ArrayDeque loop with a visited-folder set, so already-seen folder IDs are skipped instead of re-entered forever. Acyclic trees should behave the same; cycles terminate with each folder listed once.

Adds whenFolderRelationsContainACycleThenGetFolderBranchTerminatesWithoutDuplicates, seeding a cyclic folderA ↔ folderB relation via DAOs and asserting getFolderBranch completes with expected folder and bookmark counts.

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[Asgabani]

Hello Team,

Please check the changes and if you satisfied with the changes , approve them and let me help make our duckduckgo better

Thank you
Ankit GabanI

@brianhall @brindy @claude @tagawa