fix: wait for watched files to finish being written (#17100)

[TapuCosmo]

Description

This makes the external library watcher wait for files in watched directories to finish being written before queuing jobs for each file.

This configures chokidar with awaitWriteFinish to wait for watched files to remain stable in size for 5 seconds before emitting its events. (https://github.com/paulmillr/chokidar?tab=readme-ov-file#performance)

This should fix issues with jobs prematurely running when there are slow writes to external libraries (e.g. when the external library is written to using Samba) and failing.

Fixes #17100

Checklist:

• 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/)

[etnoy]

Thanks for your contribution. This looks like a good change for me.