fix(server): sync all written files to disk

[uhthomas]

Description

Add flush/fsync to all file write paths including thumbnails, transcoded videos, exif writes, file copies, and backups.

See #26881 for more discussion. These changes have been split out so that the most important changes can be merged without delay (syncing uploaded files).

How Has This Been Tested?

N/A

Checklist:

• I have carefully read CONTRIBUTING.md
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if applicable
• I have no unrelated changes in the PR.
• I have confirmed that any new dependencies are strictly necessary.
• I have written tests for new code (if applicable)
• I have followed naming conventions/patterns in the surrounding code
• All code in src/services/ uses repositories implementations for database calls, filesystem operations, etc.
• All code in src/repositories/ is pretty basic/simple and does not have any immich specific logic (that belongs in src/services/)

Please describe to which degree, if any, an LLM was used in creating this pull request.

N/A

[platima]

Testing performance this morning with small and large JPGs across local SSD and NFS enterprise HDD storage.

[platima]

Testing this now, with read cache enabled so that we're focusing purely on the difference with thumbnail generation.

Have deployed the stack directly on the NAS itself so it's local storage.

Doing three runs of each to get firm numbers compared to vanilla v2.5.6.