fix(files): preserve mtimes when copying and moving

[mh0pe]

• Resolves: Consistent handling of last modified dates when copying/moving files #15192

Summary

Preserve file and directory modification times consistently when copying and moving files, including same-storage operations, cross-storage fallbacks, and recursive directory copies.

What changed

• Preserve file and directory mtimes for same-storage and cross-storage copies.
• Preserve mtimes recursively when moves fall back to copy and delete.
• Retain known mtimes across storage-wrapper renames and moves.
• Keep View::copy(..., false) as an explicit opt-out.

Why

Nextcloud already preserves the logical mtime in the file cache while tracking the backing storage timestamp separately as storage_mtime. The storage operations did not apply that model consistently: View::copy() ignored its preservation flag, recursive storage copies dropped the flag, the local fallback dropped it, and the known-mtime wrapper read timestamps after paths had moved.

The copied or moved node now retains its content chronology while the destination parent's mtime and etag still record the operation. Directory copies restore mtimes bottom-up in a post-copy traversal, avoiding a public IStorage signature change for third-party storage implementations.

Validation

• Affected PHPUnit suites: 622 tests, 2,259 assertions, 3 skips; all passing.
• PHP syntax checks: passing.
• XML validation: passing.
• PHP CS Fixer dry run: passing.
• git diff --check: passing.
• Psalm reported 16 missing Imagick symbols outside the changed files; no Psalm errors were reported in the changed production files.
• On the previous equivalent PR head, 195 of 227 check runs passed. The nine failed jobs were Cypress/Playwright policy gates, their downstream summaries, or runner-level npm permission failures; no backend, storage, PHPUnit, lint, or static-analysis test failed.

TODO

• No remaining implementation TODOs.

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 — not applicable; this is a backend-only change
• Documentation (manuals or wiki) has been updated or is not required — documentation is not required
• Backports requested where applicable (ex: critical bugfixes) — not requested; the target is master
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component) — maintainer action required
• Milestone added for target branch/version (ex: 32.x for stable32) — maintainer action required

AI (if applicable)

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

[mh0pe]

Friendly maintainer ping @Altahrim @salmart-dev @leftybournes @come-nc — this is ready for review. It preserves mtimes across same-storage and cross-storage copy/move paths, including recursive directories, with focused regression coverage. Please let me know if you’d like any additional validation or changes to the scope.